its not a fixed number!
but more delegates mean more costs. so you have to make a choice between decentralation and costs
It costs far less to host a delegate than it costs to mine a proof of work crypto, so I disagree with that being a negative factor.
What is a negative factor is how on earth we keep track of more than 101 delegates, and make it easy for everyday users to vote for such a large amount of delegates.
Perhaps in a couple years time when delegate campaigns are far more common place and highly competitive, we'll have figured out a good way to expand above 101 delegates.
What i'm interested in, is whether it's possible to merge mine another dac onto the btsx blockchain? And if it's possible, is there any room for sidechains/tree chains to unite dacs instead of a dac being an entirely new system?