Hello, that’s because getting into and preparing for Random PvP is much easier. You don’t need any Pokemon or story progress. Basically, anyone can take part in Random PvP without playing the game beyond that. That’s why the rewards are much lower than for Normal Ranked PvP. I’d also like to point out that since the release of the PvP Chests for the Win of the Day and every additional four wins in Random PvP, activity has increased by almost 400%, and that number has stayed consistent ever since.
Right now, there are no plans to give rewards for the top 25 during the season.