That was a little of it but the patents expired years ago. The big blockers I saw were basically that it was a very complex format with a specification behind a paywall and no good open-source implementation or test suite. Interoperability was bad until a couple of years ago and it took significant amounts of complex code to make it fast enough to use.

They've subsequently improved that — OpenJPEG is quite good now https://github.com/uclouvain/openjpeg — but probably missed the window for adoption barring a major upset, which is a shame because it's a very powerful codec and has some neat tricks like progressive decoding (imagine if you could have one file in storage and your responsive design simplify specified the HTTP range requests to get for successively large resolution images?). You could ship it in a browser using WASM but I think the browsers are — not without cause — being really reluctant to add new formats and the ensuing security risks without a good reason, and without browser support no format will be more than a niche.