It's really hard to clean up media. You have to go into every single chat and from there go about deleting stuff. At least they finally added a "select all" option in there recently.
So the size of it just grows and grows and grows until it's using all the space on your phone. Not a good fit for non-technical types.
Secondly, no web view. There is the desktop app yes, which is flaky, slow and wants to update every day or two.
I just can't see average people putting up with those inconveniences and that's just a couple of them.
People behind Signal have a very corporate approach to their app where a permanent "no" doesn't exist when it comes to user choice - all what you have is "not now".
Then there's linking devices; it's not permanent but temporary and devices are removed automatically after 30 days. You can't even log into your account with tablet any more - that was replaced with linking. Cross-platform synchronization - didn't work for me at all despite being a loudly announced success.
This is at least an improvement over WhatsApp, which removes core functionality (e.g. creating groups) when this access is refused