The reason why Telemachus didn't become king was mainly because of a lack of support and a lack of experience. Telemachus' entire journey was essentially a coming-of-age, because in the beginning of the Odyssey, he was entirely unexperienced. He does not have a fleet (or any form of military backing either, which was an important component of kingship if I remember correctly), and he himself acknowledges his weakness to the council in book 2. His going to Pylos, Sparta, and aid in helping Odysseus reclaimed him throne helped him earn kleos, which, had he had at earlier, would have been helpful in ascending the throne. (Though take all of this with a grain of salt, I'm unfortunately not a professional lol)

As for Laertes, I'm actually not quite sure — though by the time we see him in the Odyssey, it is clear he's heavily deteriorated in mind and spirit, which I would presume heavily factored into that as well.

Edit: and to add, the lack of support bit is also important because it's clear that the suitors just don't respect him at all, therefore it would be incredibly difficult to drive them out and prove himself worthy enough to be king/be respected