It should be, though rules-as-written it may not be apparent.
Tactics definition: per the OP and dictionary, I take this as the art of pre-combat awareness of how best to utilize terrain and positioning against an enemy.
While dice are used to create tension and drama, combat is a lot more exciting if players feel they are free to unleash creativity (even if it doesn't always work) rather than work in a +2 here or a 1d4 there. However, there isn't really a reason for PCs to do so thanks to
encounter balance suggesting all fights are winnable. PCs don't have a default incentive under basic game design to not simply run in.
@overgeeked chimed in as I was typing and nailed why players may unconsciously shy away from tactics thanks to a "charge in blindly" assurance due to the encounter calculator and, relative to prior editions, (1) harder-to-kill characters and (2) less instant death effects.
My solution is I don't always toss fair battles at the PCs. While there is the unspoken agreement between DM and Player the DM will use level-appropriate material, I don't believe it's realistic everything the PCs stumble across is magically tailored for their levels, and I don't plug everything into a CR Encounter Calculator. My players know this, and I know they in return work on more creative, tactical ways to approach conflict than the usual
"we charge in because we know the fight is winnable."
It's a win-win cycle. Last session it was five 11th level PCs vs. 6 CR9 Ice Giants (frost giants with regen 10 using the A5E giant stat blocks which are more kickass) trashing one of their villages. A face-to-face battle, not a smart idea, but they couldn't run away from this one. So, they got creative, and not one PC went down.
The Book Way
Creative tactics may not be apparent in the books because (1)
encounter balance suggests all fights are winnable, (2) it's often more effective to use character abilities to pummel the enemy down than use tactics, (3) many maps don't have terrain features worth interacting with, (4) players may not have awareness or care that they can get a +2 to AC with light cover, and (5) it's a lot of work for the DM to work in a scenario that requires a strategy MacGuffin (e.g. the dracolich uses its captives to empower itself and the PCs need to destroy the cages).
Thus, tactics can easily fall by the wayside absent specific incentive wherein if tactics are not used, loss is suffered.