They were ordered to make ENT while VOY was still on, that's why Ken Biller took over VOY in the last season. Still under contract.
And they didn't have the degree of control that JMS had over all his work (because he was the actual creator of the B5 universe) so his strategy wouldn't work for them.
As for the "DS9 was good because VOY sucked" thing, that's another lie. DS9 had its freedom due to being syndicated, not because VOY took all the attention. Berman was as involved with DS9 as he was with VOY.