Terms like that matters more for some services than for others. For something like Spotify or Netflix, if they terminate the agreement it doesn't matter much. You lose access, but there was no accumulated value. So you can just go somewhere with only minor inconvenience. Whereas on Steam, if they terminate the agreement then you could lose decades worth of accumulated games from your library - which could be very valuable. So that's a big difference.

Now, it's unlikely that Steam will just press delete on everyone's account. But we can imagine a very profit-hungry leader taking over Steam and deciding to put the squeeze on their vast user-base. There are many things they could do; such as adding ads, requiring 'consent' to include spyware on your computer, or charging additional fees. Long term users would not be in a position to refuse these things, because their Steam library is being held as collateral.

If you trust that Steam is never going to give you up, and never going to let you down, etc. Then there is no problem. Things are currently going fine, and they may continue to be fine for a very long time. It's just a matter of trust, and power, and hedging.