Why haven't the tyranids just adapted to everything yet?

At this point they've encountered pretty much every race and beat all of them at least a few times. Why haven't they adapted to everyone's weapons and tactics yet? Why even bother with shitty ass gaunts when they can just spam space marine legion style swarms of warriors and zoanthropes. Hell, why even bother with weapons beasts at all? Massive clouds of those toxic spores and phage cells would kill everyone and render the world fit for consumption without any need for war at all.

They don't just transmit genetic data.

All those 'nids dead by flamer?
Dead, can't adapt.
Those who survive?
Adapted.

The other fleet the other side of the galaxy?
Has no idea about it.

I never understood this part, if the hive mind is one being and can create the same beasts across hive fleets, why do they need to physically obtain the genetic material?

unless you are a creationist you cant just EVOLVE! all your problems away like some kind of mgic serum, otherwise the tyranids would basically be the kid from cops and robbers who yells "wow you missed by a mile" despite having your gun up at his chest

because that's how it works.

the internet allows everybody to know everything. but not everyone has access to the raw materials in order to benefit from all that knowledge. and you still have to practice making the new thing you learned about.

so the hivemind could transmit the idea of making heat resistant carapace. but until the extreme temperatures are experienced, and evolved to counter, the bugs of that fleet will continue to melt/burn.

and aren't different fleets essentially different minds. so they would need to meet up - to a certain degree, in order to communicate?

because being perfect at one thing leaves you weak to other things, EG. If you become perfect swimmers, you suck at land combat.

>different minds
Does that mean one fleet would try to eat another fleet?

This has happened before. When two distinct hive fleets encounter each other, they fight to the death.

The stronger survives and no material is lost, so from an evolutionary perspective it's a no-lose scenario.

Wouldn't kill Orks. They're literally made of toxic spores.

In fact, there's a world where Orks and Tyranids are locked in a seemingly-endless stalemate of evolution. Purportedly some of the Orks are large enough to be seen from space.

Probably because they were both design by an intelligent creator (the Olds ones) to fight creepy metal skeletons, warp parasites and star gods.