Also, the butterflies of late Rome are just much easier to handle than those of early or even middle Rome. So much of post-Roman Europe is defined wholly or in part by Rome's invention or take on various institutions (how do you translate "jurisprudence" into Gaulish? Punic? Vasco-Iberian? - and more importantly, how would the beliefs or systems those words denote actually look in practice?) that any early Rome TL needs a massive amount of description, which can sometimes be indistinguishable from worldbuilding.
If Rome is destroyed during the Latin Wars, say, do Germanic and Slavic peoples still make their Great Migrations? At the same time as OTL, or sometime different - and why? How do the Celts of the west end up, living as they will "on their own terms"? Do Germania and Iberia have anything at all in common, as they did in OTL, or will Europe without a Romanosphere be divided between a bunch of mutually-incomprehensible religions and cultures? These are really, really hard questions to answer, because 1) Rome shaped all of them and how we think of them today, and 2) because the processes in OTL involved literally thousands of big historical events, practically none of which are well-attested in writing. It's all pretty much up to how well the author describes these events in ATL, rather than any kind of plausibility inherent to them - and that's a tough "cross to bear" (note Roman butterfly).
Of course, this isn't just limited to Europe, and big ancient PoDs in China or India would have just the same unrecognisable result. It's just that forums like these, the vast majority of whose membership is European or Euro-American, are far more forgiving to timeline slips there.