It is similar to the lack of a perfect MS Office with full VBA support, or the lack of well-designed CAD software for 21st century or the lack of industry-grade photography software someone can earn a living from, or the lack of reverse-engineering software that has the exact integration and full capabilities of IDA. It is sufficiently hard to get it right, so people who are smart and determined enough to solve PDF editing problem are asking for a return on their investment.

PDFs are final produce of a rendering process. They don't have nice text or image elements you can move around as a unit. The rendering process explodes the source material into thousands of unconnected objects. Fonts are separated into their glyphs so you need to have legal access to a bunch of very expensive fonts to just to write the correct heuristics. You need good algorithms to reverse the layout and even reverse engineer entire documents to rearrange text content. It is stupidly expensive to develop in and hire for this niche. So nobody will release their very expensive heuristics in the wild.

Btw, closed-source alternatives to Acrobat exist. I like Tracker Software's editors a lot. There is also Foxit and Master PDF. The latter two work under Linux but their UI can be janky since they ship their own UI libraries.