When the Cold War ended in 1991, the army took stock and decided that its future combat vehicles would be smaller and lighter, relying more on missiles, better communications and lots of electronic gadgets. All this was called FCS, and it would change everything. Then came 2003, and three American divisions invaded Iraq and, within three weeks, had seized Baghdad and conquered the country. When the dust had settled, and the battles were carefully examined, it was discovered that the key to rapid victory were the "obsolete" M-1 tanks and M-2 Infantry Fighting Vehicles, doing what they were designed to do.
This didn't faze the FCS developers, for the 20-30 ton FCS vehicles could have done the same thing. The key was being resistant to the RPG rockets, which the M-1 and M-2 were. But that got people thinking. We got all these M-1s and M-2s, and money is tight, and the FCS crowd are asking for over $100 billion to buy new armored vehicles that might not be as effective. Why not just keep upgrading the armor we got, and we know works? This bold idea, reeking of practicality and thrift, received a cool reception. The FCS proponents had spent years of effort to get enough political support for the money to start flowing. And now these retards, with their experience in Iraq, want to face the future with refurbs? The "retards", in the end, had the stronger argument.
When the Persian Gulf War ended, I strongly objected to the idea that Desert Storm proved that heavy armor was obsolete (and Military Review picked up one article of mine on that topic, which you can get to through this post on the Abrams).
Here's a nice long piece on the development of the M-1.