Several problems with cruisers:
First, they require 5 labs....that's a pretty hefty investment for a frontliner (the labs, the logistic slots, the tier 5 tech)...you certainly can't rush HCs unless you have early feed or are next to a noob....you can still try to get them early, but problem is that diverting resources into HCs probably is going to leave you too vulnerable for too long (feed can change this somewhat)...
By the time most frontliners could safely get HCs, others players are likely going to be breaking out the units that counter HCs, such as bombers or hoshikos....
Even if you are getting feed, HCs are slow to build (per fleet supply basis)...Illums and Kanraks or LFs in general build much faster per fleet supply and thus allow you to reinforce battles more effectively....
The most common time you'll see HCs is if an eco player starts fleeting to assist a frontline....