It's not that few have heard about it, per se.
It's more that there's an intense disinformation and misinformation campaign about it. Run largely by people who should be celebrating the victories that have been made, but who instead just handwave away all progress as insufficient. Because they really, really, really hate Biden, and so accepting that he's good on an issue (which he just plain is on climate) is not compatible with their worldviews.
You'll see it in this thread just as assuredly as anywhere.
Where yo WON'T hear it is among policy wonks. The IRA is celebrated in serious climate circles. Just listen to, say, David Roberts (http://volts.wtf), for example, and you can barely get through any segment without talking about how much it has unlocked renewable spending/expansion.
And it's not the endgame, it's just the first step along a new path. It's even built into the law that it will make further efforts politically and financially easier.
Meanwhile, people who claim they care deeply about climate don't even know what the IRA is. I'm not one to gatekeep, but it really does show how shallow climate reporting in the greater media landscape is.
The irony is, refusing to see how much progress has been made on climate under Biden may condemn us to lose it all when Trump gets reelected as a result and follows through on his promises to reverse courses on green energy in all its forms and vastly scale up drilling and LNG. Because Trump would potentially be able to cripple the act and the institutions it created even without control of congress.