Why was Data never promoted?

[varek]

I think it mostly depends on Data's ambitions. Being in a familiar environment with people he was familiar with and still learning probably mattered more to him than a promotion.

We saw in "Redemption II" what happened when he got transferred to the Sutherland.

Unable to "connect" to its crew he was forced to pull rank at almost every moment. Surely he understood that he still lacked certain capabilities to deal with other Starfleet officers than those on the Enterprise-D.

Bob

I agree. In fact, it was almost as if everyone forgot about the possibility of promoting Data. As an android, he probably did not feel slighted by that, but it was very unfair.
If they could have put Data on a ship with other androids, he would have been fine. But, he was practically unique.
He might have fared better on Jupiter Station, where they had a cybernetics lab.

 

[Armored Saint]

That doesn't sound too likely - previously in this thread, Data was compared unfavorably to Worf and LaForge, who both got multiple promotions despite constantly sinning in various ways. Worf murdered people left and right, or tried to; LaForge abused the ship's holo-resources twice with near-disastrous results.

Black marks apparently don't result in significant delays of promotions. A month or two from naughtiness wouldn't explain why Data went without a promotion for closer to two decades.

I don't think either the incident in Pen Pals had a serious impact on his career. If it had been the case, everyone in the senior crew would have been demoted to ensign before the end of the 7th season.

Obviously, you have to wait longer before being promoted full Commander than being promoted full Lieutenant, except if you're a rising star as Riker or Shelby.