You paid money for it but don't legally own it and it can be revoked from you at any time
Depends on the country. Atm a precedent could easily be set against Steam themselves in Europe. It's already been done against Oracle in conditions far more favourable to Oracle so I don't see how Steam could win.
In Canada Steam would probably win unless some tearjerking opposing side could be found compliant with Canadian Current Thing and the whole cancon flavour of thing.
In the US it's hard to be certain. On one hand, right of first sale is pretty fundamental. On the other hand, screwing over individual Americans with legalese is also fairly important to the US. Plus they have the Warden precedent making a mess of software ip law which would support Steam's case.
East coast American capitalists, beyond the reach of Mother England, did some vibrant capitalisms unrestricted by the need for British licenses or the need to pay for them.
West coast American capitalists, beyond the reach of eastern States, did some vibrant capitalisms (especially Hollywood) unrestricted by the practical need for etc.
it’s something courts made up
I thought it was made up so that the King could control what was going on in his kingdom and reward his allies.