Languages don't really become systematically simpler over time, or they would've had to start out incredibly complicated. They have some tendency to cycle between lots of grammatical forms (like Latin) and few grammatical forms with lots of helper words (like English).
("Simple" and "complex" is debatable; English's snarl of helper words is infamously hard to learn.)
It's obvious how you go in the "less inflection" direction, but how do you go in the "more inflection" one? The answer is that you start with helper words, which evolve into enclitics (fragments of words attached to other words, like the n't in 'can't' and 'shouldn't'), and eventually those become suffixes and prefixes, and then merge into the words they're attached to, creating grammatical inflections!
This process is where all(?) of the grammatical forms in Greek/Latin/etc are thought to have come from, afaik. Proto-Indo-European, one of the earliest languages we can reconstruct, seems to have been pretty close to the apex of this process, having just consolidated a bunch of enclitics into grammar.
So the goofy internet 'verbn't' trend is actually a possible glimpse of how English could acquire a negative verb form like Japanese has!