On top of that D&D is sadly a combat focused RPG - you see it in the class progression and focus on combat abilities.
For martial classes, yes. But arcane and divine spellcasters, rogues have lots of non-combat abilities. For example assasination rogue lvl 9 and 13 features are about infiltration and creating false identities rather than raw combat strength. Also almost every skill is used mostly for exploration or social encounters instead of combat. If DM lacks imagination and can only do dungeon crawl campaigns it's his lack of imagination that turns DnD party into a tactical wargame.
Assassination rogue is a combat build. It works with surprise, but even that is (RAW) limited to what a rogue can do in combat. You can't even slit someone's throat while sleeping and be sure they die if you follow the rules. You can even survive falling from extreme heights once you have enough levels (no spells needed). Can your DM rule those things possible? Sure. But D&D doesn't have rules for it beyond empowering DMs.
But perfect example are the 'creating false identities' - compare the rules for creating a false identity with a single strike in combat. Other system go into much more detail for that.
You can run D&D outside of combat, but its not made for it, no matter how much I would love to. I don't do dungeon crawls, I don't count experience points, I prefer narration focused games where you can limit combat to the most meaningful situations - D&D simply isn't the best system for that even though it has it in there to some degree. Like Kendaric said - it comes from the history of the game's development and its at its core to this day.
