Why did Paramount think they could chain their successful franchise to such a patchy network, when the franchise did very well in syndication? Broadcast television was already well into its drawn out decline by the mid 1990s.
Paramount had been thinking about launching its own network for quite some time. Warner Bros. were thinking of doing the same thing - hence UPN and the WB, two tiny little networks that ultimately failed and then merged into one even smaller, more pathetic network that's failing called the CW.
Star Trek seemed like a perfect launching pad for UPN. In January 1995, when the network launched, Trek was at the height of its popularity. TNG had just wound down a very successful seven-year run and had transitioned into feature films. DS9 was on the air and doing well. The studio wanted to use a new Trek series to help lure in viewers. And let's face it - VOY was the only series to really survive on UPN. It's one of their only success stories. Nearly everything else they attempted failed miserably.
It's just unfortunate that the network - and ultimately the producers - forced the series to abandon its premise and become "TNG lite".