There was no CGI on TNG until the crystaline entity showed up.
Well, yes and no. The "Q Wall" effect in "Farpoint" was pretty clearly computer-generated. But you're right that CGI was only used for occasional things like the crystalline entity, the space creatures from "Galaxy's Child," etc. It wasn't until late DS9 and mid-VGR that motion-control starship miniatures got phased out in favor of CGI models.
JustAFriend is on the right track, but is confusing one technological shift with another. The difference is that BSG's effects were shot and composited on film, whereas TNG's effects were digitally composited on video. This was a quicker, cheaper, more versatile technique, but it had resolution problems at the time, so you could often see distinct scan lines. Animated effects such as phaser and tractor beams were also created using video/digital equipment instead of traditional cel animation.
Also, I think there was a difference in approach. BSG made a large library of stock FX shots and recycled them over and over. Virtually every space battle was just the same flyby and weapon-firing and explosion shots cut together in a different order. So they made a finite number of shots that looked good and kept reusing them. With TNG, they also had a stock library, but it was a library of raw
elements (the individual components of an FX shot) rather than finished shots. When ILM produced the FX for "Farpoint," the TNG producers had them create some extra
Enterprise elements that could be used as an FX library for the series as a whole. But they composited these stock elements into lots of new shots, far more than BSG used. So they made a different compromise between quality and versatility.