I wouldn't call it ignorance or laziness. The Army can call a fork an "eating utensil, four pronged, with handle." It's still easier to call it a fork. I use the old phrases in casual conversation, but in a formal setting I use the proper terms. This might be your pet peeve, but we do the same thing when it comes to other areas like MOS titles.
Not knowing that your branch category changed 5 years ago is not a case of avoiding a tough and cumbersome new term. The term "operations" is in no way confusing or cumbersome. In fact, the new terms are easier. "Force Sustainment" makes a lot more sense to the average mind than "Combat Service Support." It's laziness, and it pervades the institution.
It's ignorance, just like ignorance of basic wear of uniform items and complete failure to understand your own doctrine. Ask 10 captains what doctrinal manual governs their own unit's operations, and half of them can't even name it (pro tip: if you want to be taken seriously as a professional, you should know those simple things). Try it, I implore you. Then prepare to be dismayed. Ask your average officer to draw you the NATO symbol for their own battalion on a piece of paper. The most basic bits of our own knowledge, doctrine, and structure elude us. Then again, when can't get officers to maintain weight standards or get a 300 on a PT test (or even take one, in many cases) so there should be little surprise.
It's laziness and willful ignorance. You don't even have to go to a bookshelf to find manuals now. You can carry them on your phone. The excuses have vanished, but the lack of initiative and professionalism has not.
So, youngsters, dig into your manuals now. And when you're an infantryman and find out you're going to Fort Hood, you'd better make FM 3-90.1 and FM 3-90.5 your bathroom reader. If you're an aviator-to-be, dig into FM 3-0.111, and learn FM 1-230 and AR 95-1 cover to cover and back again. Be the one who gets it right.