I suppose we're talking about two different things and two different cities. Littleton has issued a wide range of variances under the guise of PDO's (planned development overlays). If we're discussing Denver, one could point to a lack of common sense regulation/variances to restrict unfettered and harmful development. Slot homes blew up in Denver, you can see the satellite view below to show how just one small series of city blocks is being inundated by row homes.
There is also the number of permits which showcase just how big development has been in multi-tenant applications:
I know of the developer you're speaking of for Littleton who was told no — if it's the property on Nevada street that was rejected tail end of 2018. He was asking for multiple variances (height, parking, and set back) and the only reason he wasn't given the go-ahead to build was the city just passed new design standards. If this is the same guy, he asked (or paid) 15-20 strangers who didn't live in Littleton to come speak in support of the project. He claimed to be a "community and neighborhood man," meanwhile none of the people bordering the property (myself included) had ever met or seen this guy. There were sleazy attempts to suggest the property would improve safety by adding a sidewalk to a dangerous section of road (a side street with no traffic that led into an ally way). Adding to the façade was the attempted argument he was providing "affordable" housing... for 5 units that were easily 650K a piece. Now the property is sitting there over priced, windows boarded up, yard destroyed, debris outside.... looks awful. It's easy to see why communities have a bad taste in their mouth with developers and slot homes when that's what they endure.
The developer next to me is out of state — he felt the only tree on my property was in his way. So he had his guys trespass my property and cut down a 60' Elm tree in perfectly good health. It provided me the only shade and privacy I had from the development. He refused to pay me for damages and I had to sue him. The other developer behind me felt my driveway would be a great place to park his 20' trailer. When I'm not home they drive cranes and lifts into my driveway, I've had to install security cameras and call the police (and to be clear, I'm not a grumpy problem-seeking person, I'm mostly relaxed and hey, let people do their thing). The developer to the West of me installed a porter-potty on my property in my backyard — because it was more convenient and out of the way. To be quite honest, most the developers I've run into deserve the reputation dished out.
Per the city, you are absolutely right. Density = Tax Dollars. Anyone living in Denver should come to expect development, and I'm no different. I support development, so long as it's planned and retains some inkling of consistency with the existing aesthetics of the neighborhoods. This is why ADU's are such a great option for residents. It's a great compromise that permits density while retaining existing character — it doesn't sideline residents and it typically delivers somewhat affordable housing. I think cities need to expedite the process of removing ADU restrictions.