I co-founded the company that set up the ".name" TLD as part of the first batch of new TLDs back in 2001, and we had no ends of problems because of that.

A lot of people either had hardcoded lists, or they checked the length and refused TLDs longer than 3 characters. We kept e-mailing people about it, and kept getting messages back from people who had "fixed" it by adding just us (we'd generally have pointed people to articles listing other new TLDs too, to make it clear to them that this wasn't just one TLD), or increasing the limit to 4 characters... We quickly gave up on trying to get these people to stop having useless checks and settled for just getting them to accept ours.

It's quite shocking people still haven't learnt even after the number of expansions since.

I recall doing something similar for .coop

It's because a lot of regex validations (including earlier versions of Angular) have a regex that ends in something like

\.[A-Za-z]{2,4}$ (this is the end of the regex in Angular 1.15, it also doesn't support brackets or quotes in the local part, poor showing from Google)

At the time when they were written, gTLDs didn't exist, so the longest a tld could be was 4 characters (.info, .mobi). It's pretty piss poor futureproofing to be honest.

Angular didn't even exist when the first expansion happened, so either they were flat out ignorant, or they copied an earlier regex without verifying it (.museum was part of the initial batch of new gTLDs in 2001)