So I was reading the reviews of a water heater on home depot and one guy was bitching about having to hacksaw the plastic down to level with the pipes. I was like WTF. Hacksawing on a brand new water heater...
So I go buy one and new hoses and go to install it and with the plastic sleeves in the water heater nipples and the washers in the new hose, the nut on the hose won't reach the threads on the nipples. So I tried the old hoses and they fit so I used them. Took the new braided SS hoses back to HD.

WTF. Why do they put those plastic things in the nipples? Apparently other people have found out that the hoses won't fit either.

When I got the old water heater back home (I was at a somebody else's house doing the install) I noticed one of them looked like it had been hacksawed also. Is that what you're supposed to do? I used to do water heater installs all the time with my dad and never noticed this issue.

I have installed 3 water heaters in the last 2 years and here are my observations: (note: these are in solar water heater systems)

1. I never needed a hacksaw
2. Some had weird plastic inserts that I just removed and discarded
3. I used both braided  and corrugated copper hoses and did not have a fitting problem.

The plastic sleeves are just thread protectors.

Or dielectric nipple if sow leave them in. Next time buy a Bradford White much better water heaters.

How long do hoses last?

Our first water heater lasted 27 or 28 years.  Not sure if "hoses" would have lasted that long.

Or do people that use hoses replace them ever few years?

This isn't This Old House with their fancy laid out mechanical room...  :)   All I've ever seen or used is galvanized pipe or copper pipe. No "hoses". That's for the washer  :)

I'm a master plumber but I don't do much plumbing work myself these days. The last couple of WHs I did instal had those in them. I couldn't get the flexes to stop leaking with them in so yeah... they were removed. These were in my own house and the heaters work fine.

How did you remove them? I didn't try, so I don't know if they were in tight or just sitting there.

It had/has bendable copper tubes now. What they sell at home depot is braided stainless hoses. I wanted to replace them because they didn't sell a WH the same size as mine, so the new one is 8" lower and the tubes wouldn't reach. I ended up putting something under the heater to raise it up. As far as how long do hoses last, I don't know but we use braided SS hoses on faucets in bathrooms and kitchens and toilets. I know people sometimes use rigid copper on faucets but it's such a bitch to work with that I always buy new hoses. Never heard of them leaking.

The one and only time I used the braided hoses on a water heater, the hose failed and cost me several thousand dollars of damage to my basement, as well as ruining the finish on a couple of firearms.  Water all over the floor and steam/mist throughout the basement.  An expensive lesson.  I sweat in new pipes and valves on all water heaters now, whether it be for customers, friends or my own.

I think I just grabbed them with a pair of pliers and pulled straight up. I think they're only about an inch long

Not sure what you pulled out, but it was most likely a heat trap insert, which they have to install because of government energy efficiency standards.

did it look like this?

Neither of mine had the cross piece, but the old one did look like it had a rubber flap in it like that.

Yep, that's what I pulled out

Those plastic things were .gov mandated nanny Karen heat traps.

The threads on SS hoses are shorter than the brass ends on the flexible copper. So they never catch. Had it happen years ago. Never thought of using a hacksaw