[frandroid]

Because otherwise the client will be in jail before their lawyers know what's happening because the prosecution had all the time in the world to prepare their case before laying down charges, and overworked public defenders need time to build a case to defend an already built case?

[ck2]

The state often has near unlimited resources to prosecute a case, if given extended time they can come up with all sorts of things.

Speedy trials protect the defendant from rotting in jail without charge for years which is happening more and more now.