English pronunciations do change, have changed and will change in the future.
What’s happening in American English’s pronunciation of the word Comfortable?
You can call it lazy, or you can call it efficient, but American English tends to eventually reduce or even delete sounds that aren’t really necessary for comprehensibility.
This happens to words that are used often.
The first stage in a word’s mutation is to relax/reduce the vowel in an unstressed syllable to a schwa [uh]. The second stage is to eliminate that schwa-syllable altogether. This can happen providing the word’s acoustic form stays very similar to the original. Here’s an example.
Comfortable [COM.fer.tu.bll, or COM.fu.tu.bl] has the following stress pattern or rhythm: DA.du.du.du (STRONG-weak-weak-weak)
It’s mutated form [COMF.ter.bl] has this stress/rhythm pattern: DA.du.du. (STRONG-weak-weak)
The sounds that have to remain in this word, for it to be recognizable by a listener, are KMF.T.BL
The stress pattern that has to stay intact is STRONG-weak-weak.
Everything else can be elminated and the word would still be recognized.
And sometimes that’s what happens.
Other words like this are: chocolate, separate, camera.