Having worked as both a software developer creating CMSs and an editor of writers working in a CMS, I’ll tell you why so many CMSs strip out formatting. It’s because common tools like MS Word turn the HTML into garbage like <span type=”beelzebub” id=”FEruhaeiouwrghjahsbfajhdsfaadsjhfvjhfa” style=”font-size:ginormous”>. We try to strip that out automatically because otherwise it makes everything look like trash.

That said, they can handle this a lot more gracefully, but no one in media seems willing to invest in high quality CMSs as a product. They all seem to use some hellscape mishmash of outdated and poorly developed junk.