The simple answer:
MPEG-TS still exists because it’s still the best media container/transport system in existence.
It was designed and has evolved over a long time based on solid foundations by very smart people in the industry, across multiple institutions and professions.
As opposed to the “format du jour” that was quickly thrown together by some eastern block script kiddie who saw the basic outline of an AVI file and figured they could do better…
Case in point: MPEG-TS has scaled from DVD across BluRay (and DVD-HD) is the backbone of both satellite and terrestrial digital broadcasting.