Is it not more likely that a big enough mining farm mines to a lot of different reward address, making it appear as many small solo miners?
What would be the incentive?
A very large miner who want to stay low profile (i.e. not advertise to the world that he has massive mining power) may prefer to appear as a lot of smaller miners. The same way one may prefer to hold large funds across multiple addresses with lower values rather than some large amounts on one or very few addresses. The blockchain is public.
I have a harder time understanding why any "solo miner" would pay 2% to some "service provider" rather than mine on its own.
https://solo.ckpool.org/ lists several use cases.
The lottery one is the only one that really makes sense to me,
A last resort backup also make sense to me,
But in my opinion, neither do not satisfactorily explain the several blocks found recently.