They simply didn't bother to take the extra mile and it shows.
Let's see, Vicarious Visions:
-included cut levels from original game
-included two original stages, for free
-made Coco playable in nearly every stage
-added time trials to every Crash 1/2 stage
-added global leaderboards for all time trial challenges across all three games
But they "didn't go the extra mile" I guess.
Also, Crash 1 is a very special case in that many jumps and distances are built to the pixel with Crash 1's moveset in mind. The extra movement and abilities would mislead players into using them on stages that weren't at all designed for them, as well as interrupting the faithful nature that they were meant to be played in. Things like the double-jump/spin jump/bazooka abilities would completely break the difficulty of the first game, as well as opening up frustration to overshooting jumps and timed platforms. Sonic isn't really comparable since the movesets and stage layouts allow a lot more freedom of movement, error and course correction, even in the old stages with new abilities. Crash 1 in comparison has many particular physics/box/platforming puzzles that call for the particular timing and physics and of that specific game, that would be broken by 2/3's movies.
Something like not including later movesets in earlier games was a conscious decision, and not out of laziness, especially when VV went out of their way to include all of the extra goodies they did when they didn't have to.
