[Spoilers Main] What do you think motivated Robert to give Storm’s End to Renly?

To clarify, I am not asking why he didn’t give it to Stannis. That has been discussed many times, and people tend to think it was either a snub for failing to catch the Targaryen children (as well as Robert’s general dislike for him) or an effort to confirm Stannis as his then-heir and put a strategically important castle in trustworthy hands, or a bit of both.

However, it occurs to me that just because he gave Stannis Dragonstone that didn’t mean he had to give Renly anything:

Renly was a third son, had Robert not become king its unlikely he would have ever had a seat of his own anyway unless there was an available heiress to marry or a lord in the Stormlands died without issue and his lands returned to House Baratheon. And unlike Stannis, Renly was a child during the rebellion and did nothing worthy of reward.

There was no real risk to not giving him Storm’s End either. Even being the king’s brother, it seems unlikely Renly or his hypothetical heirs would have accrued the influence necessary to make a play for the throne in the future without lands of their own.

So that begs the question: why give Renly Storm’s End instead of just holding onto it for Robert’s future second son? Was it just generosity, or was there some thought put into it?