Part of the problem is the number of 'lottery' channels they've created.
The pot of money that people have to spend hasn't increased, so neither has the prize fund, so Camelot are just making more, smaller winners.
You used to have 1 Saturday draw, and nothing else.
Then you had 1 on Wed and 1 on Sat, and (for example) 25% of the spend went into the Wed, and 75% went into Sat.
Then you had 1 on Wed, 1 on Sat, and a daily play - so less went into the 'big' Wed & Sat draws.
Then you had a couple of scratchards, then 10 scratchcards, then 100 scratchcards, etc.
So as the number of channels for the same spend increases, each of the 'pots' decrease. Camelot prefer the multiple channels as they can incur notional 'costs' for each and make a fortune doing what Branson was going to do as a non-profit.