Nah, its more that:

(1) The standardized, broadly compatible subset was a mostly unstructured, imperative language with very limited features, only global variable scope, named custom functions limited to a single expression (and a syntax that sharply limits what can be in a single expression), variables limited to numbers and strings, that was very tightly adapted to systems without modern capability (“line numbers” seem baroque now, but it really was a great way to have a simple, line-oriented text environment that worked as both REPL and simple dev environment.)

(2) While there were plenty of nonstandard versions with more modern features, they were mostly proprietary, often tied to very specific other pieces of software, and not particularly interoperable between them.

(3) Plenty of more modern, just as easy to use for simple cases, languages became available that had broad cross-platform compatibility (sometimes, not always, with formal standardization) without the limitations of BASIC’s broadly-compatible subset.

(4) Almost no computers came with “power on BASIC” anymore, so the unique role the ubiquitous use of BASIC in this way in the 8-bit home PC era gave it and which provided a support for its overall popularity went away.