1st round projections aren’t the same as winning projections. Those 240+ seats projections were illustrating the actual results of round 1, where the far right was ahead in a lot of places, not from guessing how round 2 would end, because… we don’t do it that way, I guess? But since round 2 only brings the candidates who scored above 20%, which usually means either 2 or 3, rarely 4 candidates, instead of 10+, that means everyone who voted on round 1 for the parties that lost would then vote for one of the remaining 2~3 candidates. And that’s anybody’s guess.
So you can have 30% of voters bringing the far right to the top among 10 candidates, but those 30% don’t win when there’s only 2 or 3 candidates left, because it turns out 70 always beats 30 - especially with the mutual agreement that a 3rd place center or left candidate would drop out in favor of the other to stop the far right. This doesn’t work in rural places where the far right was over 40% (some “centrists” still chose the far right over the left alliance, getting over 60%), but it works everywhere else - and that’s what happened here. Think of 2 round voting with >10 parties as a little bit more like one round ranked choice voting than first past the post with 3 candidates.
Realistically, we knew that the results of the first round was never going to hold, because it’s been like that for a few decades - like someone else said, 2002 saw the far right fail to get more on the presidential round 2 than the 20% of their score of round 1 (but that ceiling has been rising since because of Macron); of course there’s the concern of the growing number of regions that feel abandoned and turn to the far right, but beyond that, the real question was how well the left alliance would do, and how badly the “center” would drop. That’s the big deal, the left is back on top - now we just hope that union is strong enough and they don’t collapse again because of the constant demonizing that Macron and the media have been spewing non-stop (they really no joke honestly want the far right over the boogeyman “extreme left” that doesn’t exist), with the center left abandoning ship to side with Macron again.