I'd have to say, because of the flexibility of the schedule. Especially if you are a pioneer.
Or............you like to take advantage of good cheap labour !
In my former congregation, an elder brother, had an established cleaning business, and a lot of brothers and sisters in the congregation, worked for him, including myself.
I had a dental business I cleaned on a nightly basis, and I thought I was doing OK, until I saw a cheque for him, from the property manager, for the previous month's work. He was paying me less than half of the contract's worth.
All he did was come in every 2 months, and strip and wax the floors, a 4 - 6 hour job, which I also helped out with. The cleaning supplies were provided by the property manager.
So, lining up 10 - 12 contracts like that, and getting brothers and sisters to do the work for you, and making a 80 -100 % profit, while I'd say that was pretty lucrative.