Sometimes a Steam link for a game in a giveaway sends me to the main store page

In addition to the above, it can also be pointing to an outdated version of the game ID.
Generally means it's been removed from store, though.

it can also be removed by publishers Sekai Project proved this to a point by bowing down to a couple of asses and removing yohjo simulator a few days after it was released on steam because people wouldn't stop complaining its just sad they can do shit like that

As Sooth said, about the ID, it happens, for example, when a game is released again as a "Extended Edition", or "Remastered", and they remove the previous. Or they simply make changes like, making the "Deluxe" version be the main one, then removing the one without the extras, etc.

This is usually what most happens.

Totally removing a game from the store is rarer, but also can happen.

thanks all who replied, that all explains it then.

closing the topic since my question got perfectly answered