Good excuses and hair
If you are MtF and need a manly man, socially acceptable reason to remove body hair, that's easily findable.
1. Cycling
2. Swimming
3. Running
4. Tennis
5. Bodybuilding
The search results gave a description of reasons men shaved their legs for these sports and I didn't bother to include that in part because bodybuilders will shave EVERYTHING.
Additional articles had other sports in the title, like "triathlon." Plus I found this piece talking about specific athletes.
This piece uses the term manscaping and talks about injury prevention and treatment. So any job where minor injuries might be a normal part of the job is potentially a good excuse to consistently remove body hair wherever you so please.
I have heard Muslims of both genders remove all body hair.
I had hair halfway down my back at age fourteen and went to my father's barber and got a super short man's haircut because I enrolled in gymnastics and got tired of stepping on my hair.
Dirty Jobs did an episode on people who clean the windows of skyscrapers. Most of the people on the team were male and had little to no hair on their heads. The one woman had her hair in tight braids or something.
One of the cameramen had to get his hair cut to escape losing skin when his longish hair got caught in the gears. This is when they learned the reason for the short hair: If you do this daily, sooner or later you will get your hair caught and it's a potentially seriously dangerous situation.
Veronica Lake was an actress whose hairstyle fostered a trend. She changed her hair during WW2 because the cut was causing accidents in industrial settings.
Accidents dropped 25 percent in such plants after she changed her hair. If you are FtM and doing "a serious job" to try to support yourself, short hair isn't an unreasonable choice for safety reasons.
My hair is short for hygiene reasons related to my incurable medical condition. It was even shorter when I had a corporate job and I worked a lot of overtime while very sick and was able to do that in part because I had a very minimal haircare routine.
Arguments that long hair is feminine and somehow socially required are essentially arguments that women should plan to marry well as their only hope of supporting themselves. It is, in effect, a polite form of prostitution.
If you work for a living and hope to support yourself, your job should come first. Anyone claiming that being "attractive" in a girly way is more important than being good at your job is someone effectively insisting that your primary goal in life should be getting married and putting his career FIRST.
If you LIKE having long hair, have at it. If you are FtM trans and have no plans to politely whore yourself out to keep a roof over your head and call it "love," I suggest you get a haircut and get a real job.
Though it may play better to get a real job and then cut it short "Because I don't want my hair caught in anything and wind up defacto scalped." Because my understanding is that if a big chunk of hair is grabbed by machinery and ripped out by the roots, it NEVER grows back.
In contrast, if it's merely cut short, you can regrow it someday if you ever meet Prince Charming and blah blah blah like your troglodyte relatives are hoping for.