I don't think they're lower, but they're different. Notably, Alphabet employees of the other Bets (Waymo, Loon, Verily, etc.) get stock in the bet rather than GOOG stock. This is privately held and so a lot less liquid than GOOG, and you lose your unvested shares if you transfer to the mothership. It has a lot of the same risk/reward tradeoffs as working for a startup.