True, but we saw a big spike in both consoles and game sales during the lockdown. Maybe stuff they planned to buy later they bought it at that moment.
If we look at the number of PSN users who played them, outside the 1st week sales (where TLOU2 sold way more), we can see TLOU2 is selling at the same pace TLOU1 did at the same point of its life cycle.
And after the point where TLOU2 is, TLOU1 sold a shit ton of units more. So no, TLOU2 sales didn't drop off of a cliff. It's selling very well right now and on track of selling more than TLOU1, the thing is that in the launch week it had too high, insanely rare record numbers that it wasn't possible to keep them there.
Same goes if we shorten the TLOU2 sales to the same period we have tracked from GoT: the curve is basically the same, with the difference that TLOU2 sold way more during the first week. Maybe due to hype from the previous entry, maybe because a ton of people just bought a PS4 because of the lockdown they had a few weeks ago and that was the only big PS4 AAA exclusive game released there.