TNs could be renewed indefinitely, however they're specifically meant to be temporary so you can only renew them if you continue to convince the adjudicating officer that you do not intend to renew them indefinitely. This may become a challenge a decade or two in. They are explicitly not a replacement for a green card. They can also be revoked at each border crossing.

An H-1B gives you a defined 6 year window with doctrine of dual intent allowing you to pursue a green card, which a TN status does not.

So you can get a green card and thus aren't tied to the company?

because it opens up the options to sponsor you for a green card.