"Bugs" I get, but what do you mean by "non-standard behavior" mean here?
My perspective, having had some experience with some pretty sophisticated DB adapter layers in the past: SQLlite and other nominally-SQL DBs all have only a very superficial level of SQL-level compatibility. Aside from closely related DBs (e.g. forks) it's not like there's any actual ability to exchange character-for-character identical SQL or DDL between DBs. All kinds of things like quoting, namespacing, and so on have subtly different syntax. It's pretty easy for a human to switch between SQL-x and SQL-y systems, but not so much when you're talking query generation. Even Rails has a pile of different backends for Active Record, and AR's backend is pretty darn simplistic.
It should be compatible with most DBs, but SQLite has more dynamic types, and supports more things, in ways that are "odd" for almost all other DBs. As you correctly said, in general, no two DBs are easily interchangeable, and SQLite is no exception, perhaps it is even more of an outlier in fact.
That means that to implement SQLite, not using SQLite code, means you need to carefully reproduce that behavior, and all aspects of it - in practice, including bugs - to be a compatible web browser. For a web standard, that's just unacceptable.
"Bugs" I get, but what do you mean by "non-standard behavior" mean here?
My perspective, having had some experience with some pretty sophisticated DB adapter layers in the past: SQLlite and other nominally-SQL DBs all have only a very superficial level of SQL-level compatibility. Aside from closely related DBs (e.g. forks) it's not like there's any actual ability to exchange character-for-character identical SQL or DDL between DBs. All kinds of things like quoting, namespacing, and so on have subtly different syntax. It's pretty easy for a human to switch between SQL-x and SQL-y systems, but not so much when you're talking query generation. Even Rails has a pile of different backends for Active Record, and AR's backend is pretty darn simplistic.