I think the reason Bug might not have been buffed and is considered one of the worst types (if not the worst) is that maybe it isn't so popular that GF would care about it. I believe they have earned the reputation of being the early-mon that you would always ditch after the warm-up, and unless there has been a major voice about it, it might not change.
For example, Thundurus (Incarnate) form in VGC was a menace, as its Prankster ability gave it the opportunity to spam Thunder Wave + Swagger against its opponents in Gen 5 (didn't help that electric mons were not immune to Paralysis), and that Thundurus was fast and strong. It wouldn't be a coincidence that GF nerfed him by reducing the accuracy to 90%, paralysis speed drop was halved, and Dark Types were immune to status moves set by Prankster. Or how in Gen 5, dragons were a problem since they were too powerful via Outrage + Draco Meteor, and that it had super effective coverage to deal with the frail ice types or passive steel types. That's why GF also dropped the Fairy types to combat the overwhelming fairies. Not saying the changes were perfect: Thundurus' viability in VGC dropped, and that Fairy types may be too powerful (i.e, Xerneas), but the point is to show how Pokémon can be buffed/nerfed if it becomes a problem.
And that's where the problems with bugs are, because I believe they aren't that popular:
- Pinsir and Scyther - Cool-looking single-stage bugs in Gen 1, but unfortunately, they don't even get a Bug-type move.
- Scizor - One of the most unique Pokémon due to its Steel/Bug typing, but I feel it's more remembered for being a Steel type due to how new the type was and Bullet Punch.
- Heracross - Perhaps not as popular, but it's known for its friendly nature and is a counterpart to Pinsir.
- Ledian - Is a joke
- Shedinja - At least it's unique for its ability - Wonder Guard?
- Volcarona - The Ace Pokémon of Alder, the Unova Champion. However, it might be known more for its fire type, due to how its Pokedex mentions its closeness to the Sun.
- Golisopod - Definitely a popular bug type thanks to ya boi Guzma
There are others like Ash’s Butterfree, Kleavor, and Pheromosa, but even then, that's not a lot of popular bug types, and even then, they've never reached the popularity of other favorite Pokémon. It doesn't help that Bug-type bosses aren't known for being popular, with some exceptions, such as Viola or Bugsy (a surprising wake-up call) or Guzma (a strangling wake-up call).
Compared to other weak types like Rock and Poison, they get buffed (at least in theory), as the former gets a special defense boost in Sandstorm, whereas the latter are one of the few types that can resist Fairy attacks, get a near-exclusive move in Toxic (and never miss), and absorb Toxic Spikes.
I think if GF wants to buff bug Pokémon, the casual fandom (not competitive, sadly) would need to care about them more. They don't necessarily have to be as popular as Lucario, Charizard, or Mewtwo, but at least popular enough that GF could buff them.