Development of the F60 stopped long before the races you mention. The announcement came after they already gave up on the car. And right fully so. As for the only driver out of 4: Since you're new on here you probably don't know this, but I have zero sympathy for Massa. I can't wait for him to be gone from Ferrari.
A bit of deja vu, as I'm sure I've posted this before. I'm sure I heard in an interview somewhere, Kimi had saying that up until Hungary,the F60's set up had been a compromise to try to suit both his and Massa's driving styles but but unlike Massa, he was struggling to adapt to the car (I believe his actual words were along the lines of: "The car didn't suit me and there was nothing I could do about it!"). He then went onto say that after Massa's accident, the engineers concentrated their efforts on making the car more suited to his style and suddenly his results started to improve. Whilst this was to Kimi's advantage, it was part of the detrimental effect felt by Badoer and Fisi (one of several). As for LDM and Alonso: Ever since Schumacher retired (forced or unforced!), Ferrari have been missing that level of dedication, driving ability, development ability and team leader skills (lets be honest, nice guy as Massa is, he's no Schumacher when it comes to being a complete package of a racing driver). In 2007 they looked for a suitable replacement for Schumacher and the next best in the pecking order was already taken by McLaren in the shape of Alonso. Third in the pecking order of drivers was Kimi, hard to deal with for a team, but on his day, blindingly fast and almost unbeatable. The downside?, if the car wasn't perfect he couldn't make the difference like Scumacher could in his day, which led to too many races that weren't "his day". But Kimi was too fast to ignore so they took a gamble and signed him, based on "next best available". Other drivers would be an even bigger gamble. As history has now shown us, Alonso's deal at McLaren turned out to not be what he thought it was (whether promises were made and not kept or Alonso misinterpreted the deal or whatever the truth, we'll never really know). Alonso got into a spat with the team and Hamilton and while they were squabbling, Kimi came in and stole the candy (so to speak). Suddenly Alonso became available again but Ferrari had two many years left on Kimi's contract to make it financially viable to break and besides, he'd already shown he could work with Massa and had won the WDC. Alonso on the other hand had just been in the centre of a big team dispute and might just be more trouble than he was worth. It was too much of a gamble for Ferrari so they opted to not rock the boat and stick with what they had for 2008. In 2008 Massa and Kimi work pretty well together, finishing 2nd and 3rd respectively in the championship, but although Kimi proves he is one of the fastest on track (with 10 fastest laps in the season), questions start to get asked about his comittment now he's won a title. Meanwhile, some people, even within Ferrari, start to question whether to replace Kimi with Alonso. But 3rds not bad and maybe the 2009 season will be better, besides which, a two year contract would still not be cheap to break. 2009 as we've just seen, starts off with the team hampered by a different interpretation of the rear diffuser rule, a weight shift involving the KERS batteries (from the nosecone to the middle of the car), and eventually results in a car who's aero and mechanical balance are far too compromised for the car to be very good. Ferrari realise you can't polish a turd and ditch the development early to concentrate on 2010. As mentioned above, Kimi cannot get to grips with the car whereas Massa seems to be able to adapt to it better. Then comes Hungary and Massa is out the picture. Suddenly it's far more important to have a car set up to suit Kimi's driving style than two different drivers and Kimi starts to do better, but still questions about comittmnet get asked and now his technical feedback is called into question. Ferrari realise that to develop the 2010 car throughout the season, they need a driver in the car who can give the engineers better feedback, like Schumacher used to, along with the other attributes mentioned before, and Kimi's just not that man, so they buy him out of the last year of his contract. Schumacher's already apparantly been ruled out with a neck injury and besides, does he still have what it takes? (argued elsewhere on this site ). So they look to the man they were tempted by a few years before, Alonso, who is still deemed to be the next best in the business. However, Ferrari have noted that there were problems with Alonso and McLaren and the perception of the deal he thought he was getting,compared to the deal he actually got. They also noted how it all fell apart so have decided to be very upfront, open and public with Alonso about what deal he is getting and what the team expect from him. By being this public about the deal, there can be no: "This is not the deal I signed up for!", later on. Everybody knows the score, they're all singing from the same Hymn sheet and are going to be working as a team, for the good of the team with a view to giving both drivers the best chance to be challenging for the Championship. Yes it's a gamble by Ferrari, but as they see it, it's the safest gamble.
