Lottery prizes depend on how many tickets have been delivered. When first prize was over 2 btc, there were moire than 1B tickets, most of them from bot accounts (many 15xxx winners with ~25k tickets).
Bots have been banned, so now number of tickets has decreased, so has the prizes.
Personally, I aslo suspect the site owners to have decreased prizes of lottery to finance their gambling contest. But I have no evidence about this, only my opinion.