Of course there are plenty of monetisation and engagement reasons for that UI item to be awkwardly placed…
Kaguya seems a little better here, but it too starts with a huge 'MAKE AN ACCOUNT OR FUCK OFF' message in mid screen, with the search field in the navigation bar on top. If you want become the Goodreads alternative, start with realising that a lot of people just want to see if the reviews are any good before committing to creating an account and contributing in turn.
It's just a bunch of basic usability problems like that that they've never bothered addressing.
There are other corners of it that could be nicer. It's not so much about modern tooling as much as it is about using modern tooling to achieve better flow and more pleasant presentation.
Less optimized for farming my attention and ads, more optimized for me discovering things, and not being shoehorned into choices.
I have the same complaint about BoardGameGeek. If it was super snappy to go with the dated design, I wouldn't bat an eye, but it is also kind of a slog.
Both are things I use for discovery a little bit more than I use to record my thoughts about my previous experiences, so my browsing behavior is very breadth-first search and that makes the slow loads more of an acute problem for me.