Why are you even asking this here? It was Lenovo's decision to do so.

Well, this is not a gaming computer. Throwing a GTX 1050 or 1050Ti would both be meaninglessness and more expensive as well.
Even if I agree that with a GTX 1050 could be a good idea in this notebook, the GTX 1050Ti however, makes no sens at all here as that GPU was designed for games.
I don't know when was this computer released but maybe the GTX 1050 and Ti didn't exist yet back then.