well why not make a 5th generation they still need to make a Steel and a ghost and dragon evolutions for eevee and gamefreak would probly make more in one minute then i make in one year
true but sometimes it's better to wait a while after doing something big like releasing a new gen, if they release it to fast then after a while people have seen enough of it, if they release it when it's needed then they have the oppertunity to stretch it again.
it's the same as feeding goldfishes, you can feed it when it's needed & the fish has a full stummic for a while, but if you feed the goldfish to much and it dies.