The Russians wiped out 4 Abrams tanks in 12 days. That’s not a good look for American tanks. From Mike Fredenburg at The Epoch Times via zerohedge.com:
Thirty-one M1 Abrams tanks were delivered to Ukraine in September/October of 2023 only to effectively disappear from the news for about four months. Now with the reported destruction of the fourth M1 Abrams tank in a span of 12 days, they are back in the news. And the fact they are back in the news is a sign of how desperate things are for Ukraine.

There are a number of plausible reasons that Ukraine did not deploy the Abrams and their freshly trained crews to the frontlines until just recently, and none of them are mutually exclusive.
First, while a properly supported M1 Abrams is very effective, it is highly maintenance intensive and guzzles gas. So, before they could be used at all effectively, the proper support infrastructure and logistics needed to be in place. Also, by the time the Abrams could be properly supported by Ukraine, it was facing heavily fortified lines that included tank traps, trenches, tank-killing drones, massed artillery fires, and minefields that have proved devastating to Ukraine’s other tanks. And with the failure of Ukraine’s counteroffensive, it made sense to keep the gas-hungry/maintenance-intensive Abrams in reserve for defensive operations when Russia inevitably began its own offensive operations.
All of the above reasons are legitimate, but arguably the biggest reason may be that it was believed by Ukraine and the Biden administration that the propaganda value Russia would reap from their destruction was far greater than any value they would bring to Ukraine in uselessly throwing them against the fierce and devastatingly effective defenses of the Surovikin Line.
They should just leave Bradley Square as it is as a warning to anyone else who thinks they want some of Ivan the Bear.
Hopefully they are scavenging/salvaging any useful parts before they are used in washers and dryers! (s/)