It is the only way of token interest he knows, combined with massive shitdrops.
That was also why he wants to increase witness rewards. In his, externally staked world, returns are given for staking but those returns come from the SR's production. The SRs actually reward for voting for then.
In other words: bought votes. Which, of course, is interesting to traders (but wouldn't be with our low interest rate alone).
It is interesting, and absolutely scary too, that for someone operating an almost feeless chain as well... he seems totally oblivious to the need for engagement.