I gather that the VOY and ENT casts are reasonably close too, though perhaps not to the same degree as the TNG lot. Nevertheless, certain members of those casts seemed to have issues with the shows themselves, to greater or lesser degrees; you had Robert Beltran publicly denouncing VOY and its creative forces, and the cast, particularly Kate Mulgrew, having issues with Jennifer Lien's sacking, ENT's Jolene Blalock criticising that show's direction and accusing the series of lacking creativity, and the producers of being out of touch with the fans. These factors were bound to create some tension.
In the case of TOS, you had the supporting cast's well-publicised issues with Shatner, and the DS9 set was by all accounts a very serious place; much more of a working environment. Michael Dorn, in comparing the TNG and DS9 sets, has said he feels that was down to Avery Brooks being a "pretty serious guy," as the leading actor often sets the tone.
The TNG years seemed to be a time when everything came together; a cast whose personalities gelled and an environment where everyone was pretty much happy with the working conditions and the management of the show.