Why does Hollywood keep doing sequels/remakes/reboots to old movies?

Because they are usually making money. The film business is more about making money than satisfying people.

Do you complain about the James Bond films also?

DUDE...PAUL RUDD IN UNIFORM...I AM STOKED FOR THIS FLICK.

Did you say that when Star Wars 5&6 came out? Star Trek TNG? Avatar 7?

It has happened before, and will happen again.

No need for 'proof of concept', they know it already works. Pre-established fanbase. Nostalgia/legacy appeal. Less creative effort needed/faster production time. Box office from previous installments can help decide budget.

They're playing it safe.

Because the people in charge were kids at the time the movies were big and want to do now their own dream movie.

I think it's because they own it, they may as well make money off it. Like they can definitely make a brand new ghost catching movie if they want to, but they already got an old dusty ghost catching movie sitting in the garage.

It's not that they have run out of ideas, it's that they refuse to hear any new ideas or take risks with new ideas. There are also several other factors at play, and have been ever since the 2007 Writer's Strike, and the beginning of the Woke Era in 2016:

1.) Racism; there are people in Hollyweird that are resentful that "old white men" are the ones who have been in charge for years, had some of the best writers, best directors, and best producers, and they wanted to change that, but it's been pushed so hard the other direction that you have a bunch of young, diverse, talentless hacks straight out of college who don't know jack shit about what they're doing, with childish, untalented adults as their bosses.

2.) Lack of Creativity; due to the two factors listed above, you've got a bunch of childish, untalented idiots in power that have only grown up in the LA Basin, have never left it to go experience the world, have only grown up with films we all know from the past 40 years, and have nothing else to go on. They also don't want to admit their shortcomings to the world, but it becomes obvious through their work.

3.) Appropriation; you basically have a bunch of greedy, selfish, arrogant, stupid people that see dollar signs and a possible cash cow from franchises they used to ignore and write off as "nerd niche," and they simply do not know how to milk that cow properly, and [relating to #1] drove out the "old white men" and people who loved the franchise who would have respected the source material when writing new stories. So then you have people who don't love the franchise at all, but just want to make money and "capture Gen Z," as well as niche groups that never were interested to start with, and as we have seen in the past 8 years, it's all gone over about as well as you'd expect; like a lead balloon.

4.) Laziness; relating to #2, you have the Woke idiots who don't know how to come up with new ideas, and relating to #3, greedy jerks who just want to make money and don't love or respect the source material at all, and try and twist the story into series of propaganda, since all they seem to know how to write is left-wing political propaganda about how "white men bad, WOC and gays good." Plus, the studios don't want to waste money on taking risks (relating to the intro) with new ideas, so they take older franchise they know would be money-makers, and milk the cash cow, but the wrong way, and then they don't understand why they're still losing money and pissing off the customers, including the niche groups they're pandering to.