Why would you assume that they hold the alt crap they mine?
I never made that assumption and would always convert my mined alts with my rigs to BTC as well. This was merely for "store of value" reasons however as I would never waste my time supporting and profiting off of scamcoins. Legitimate alts are fine to leverage for profit though.
If you want to discuss an alt cloud mining contract that you think is wise to invest in go ahead.
I get some alt dogs from Genesis. It´s peanuts, only .25 BTC invested. They need to lower prices by a third at least for me to put in more.