No offense, but who do you propose should do this work? FA has like... 1-3 devs, I believe; I don't know how Dragoneer buying the site back from IMVU would have effected that number but it almost certainly didn't increase it. Backend changes to make the codebase less gnarly are being done continuously, but dropping everything to re-develop the site isn't a realistic option.
The database changes alone would mean days if not week(s) of downtime (like, I am 99% sure a number was dropped on the forum some time back and as I recall it was in that general ballpark). We're talking about 50 million submissions (minus removed submissions, which I don't know to what extent they might still have any database entries), no less than 100k users (there's currently 35k users online; saying that's 1/3 of even the active the userbase is hella lowballing it), probably a couple hundred million comments, plus favorites (I wouldn't be surprised if that gets at least close to a billion - that'd be an average of 20 favorites per submission-ever, and that's... not that much given the numbers more popular artists get - I have all of 500 watchers and average around 10 or so per submission based on some really quick and dirty math), notes, tickets (with responses), and so on. Basically, it's a metric fuckload of database entries.
With the Internet culture (including the less savory bits, like "DDOS LOL") we have today there's no getting around the need for a service like Cloudflare for a site of FA's size, and to the best of my knowledge anything competitive functionality-wise is significantly more expensive.
Like, absolutely rebuilding things from scratch, having a better designed database, etc. would lead to a better version of the website existing. New technologies are available, best practices have been improved, the site likely wasn't originally built to be scalable to its current size, and so on. But actually doing it is not feasible. If nothing else so because the existing codebase isn't going to just... sit there and not have issues crop up that require dev attention while work is being done on a hypothetical new version. Having that new version would be nice. Getting there is most likely all but impossible as things currently stand.