I doubt remaking a PS3-era game from the ground up was neither fast nor cheap.It was done this way because it was fast and cheap.
I was also a bit disappointed after seeing the leaked trailer because I had it in my mind this was meant to be their PS5 showpiece debut.
However, this remake was supposedly started in early 2019, overlapping TLOU2's development. Initially, started by a smaller team within Sony called Visual Arts Service Group, after which Naughty Dog took over the development.
So it's only reasonable for the remake to look similar to TLOU2 given the timing, the development overlap, and being on the same engine.
At the very least there will now be visual and mechanical cohesion between Part 1 & Part 2.