Why didn't Sunny and Gina ever get married?

Throughout the entire tenure of the show there was undoubtedly great chemistry between Sunny and Gina, that's not to say in reality in real life Saundra Santiago had somewhat negative feeling towards Don Johnson off-screen that is. However on-screen the show’s writers habitually wrote it where there was always an "if" but never a "when" between Sunny and Gina, resulting in sort of a constant and frequent Casablanca effect. I personally think it was a big mistake not ever having Sunny and Gina get Married, I actually think it was a huge mistake that the show’s writers and producers actually contemplated let alone decided to have crocket marry Caitlin Davies and not Gina. Same thing in Season 2 episode 1 "The Prodigal Son" which is my all-time favorite episode of Miami Vice, as Miami Vice is my all-time favorite TV show , as far as I'm concerned the episode of "the Prodigal Son" both story wise and action wise could not have been any cooler and awesome as it no doubt was extremely smooth ,but as far as Crockets love interest " Margret" in the episode goes , what an absolute crime and injustice it was that they got such a ugly dog to play Sunny crockets love interest/sexual attraction. I mean My God it would have made more sense for crocket in the episode to have had no love interest or bed sequence at all for crocket and just had him strictly fought crime in N.Y.C with Rico. Speaking of which Tubbs’s relationship and love interest with Valarie made all the sense in the world, while crockets relationship with Margret made no sense at all in the world. I not only think Sunny and Gina should have gotten married I think as time went on Tubbs and Trudy should have gotten married as well. As a Miami Vice die hard, I think it's very easily imaginable to picture within either season 1 or season 2 Sunny and Rico being each other’s best man and at the same time Gina and Trudy as each other’s brides mates. And as far as Valarie goes Tubbs and Valarie did very much have a rock solid chemistry however if the show’s writers and producers were at all adamant or sincere about having Tubbs and Valarie be together as a serious "item" as they call it, I think they the show’s writers should have made Valarie a regular actual character in the show immediately after "the Prodigal son" or very soon later in season 2. Of which too I may add I think if they had done just that they could of done two (2) things number one: With Valarie in the show as a regular character and not just an recurring regular or occasional recurring regular as she really was, with her being Tubbs general love interest as Gina had been to sunny they could of slowly and gradually phased Trudy out as Rico's love interest (Not as a character) and Number Two : where they would of phased Trudy out as Rico's general lover interest I think they should of then phased Valarie in as Rico's new general lover interest. In closing as far as Trudy does go as far as being a love interest of some sorts to someone in the show (Miami Vice) I think Trudy could have possibly have been a fairly good match/ or equal flame to Lt. Castillo as it is in the show they not only were both secondary Major characters, but both dark complected characters as well as opposite sex characters allowing for there to theoretically be good love chemistry between the two. Now Lt. Castillo was married in the show first to May Ying who he thought was killed at the end of Golden Triangle Part 1 and appears in Golden Triangle Part 2 and the character played by another woman appears in the season five episode 3 (Heart of the Night) and for the most part throughout the entire tenure of the show Castillo seemed almost too honored to his ex wife to explore other women however it probably would have been very workable to have Castillo and Trudy to be an "Item" as was Sunny and Gina, and Tubbs and Trudy and Tubbs and Valarie when she appeared in the show on occasion were.