Hello, first year lab animal resident here.
Short answer: scared away from GP, went into vet school with the primary goal being to specialize in lab animal.
Long answer: was doing the pre-vet thing in college, did some shadowing at a GP, the vet I was shadowing told me not to do it (high debt, low personal life satisfaction, burnout from angry clients). I also saw some irate clients first hand and saw more of the "if you loved animals you'd fix him for free!" than I could handle. Wandered away from the pre-vet path and went straight Bio. Got a job after graduation in a lab working with mice. Met the lab animal vet, realized that was a thing (had no idea beforehand). Started getting more interested in this field and eventually started taking the pre-reqs I didn't take after I got scared off of vet med, applied, got in, did the vet school thing and nothing changed my mind so here I am! I also worked for a year as a receptionist at an emergency clinic during vet school and that pretty much solidified that I never want to work with people's pets.
Loaded question honestly and I probably can't fully honestly answer at this early stage. I'm also in a pretty specific set of circumstances that don't apply to everyone, but here's my take. In my specialty, high 5 or low 6 figures is pretty standard for boarded specialists. Most residency programs in this specialty are also at a much higher salary than the typical intern or other residencies (started at $47.5K rather than ~$30K). This field also can have the added benefit of Public Service Loan Forgiveness as an option if you stay within government or public university positions, which (if it stays in place) erases your debt tax-free after 10 years of qualifying payments (meaning you paid on time while working full time at a non-profit or government job). Finally, I also happen to have married a man who has a well-paying job in software development/architecture which contributes greatly to my financial well-being at this time. Without him, I'd like to think I'd be okay, but I would definitely be eating a lot more ramen, have a lot longer commute, and probably live in a crappy 1 BR apartment somewhere. Overall though, in this field (lab animal) it is becoming more the standard to be boarded than to not, so trying to break into the field without specializing can be a lot more challenging.
Definitely love this field for some of the things you listed above. I think my work-life balance right now is really fantastic. I work 8-5pm every day and typically don't leave too late. The latest I've ever been stuck here is probably ~6pm waiting for a monkey to wake up from a late afternoon surgery. Most of the time we don't let PI's do late afternoon surgeries because we don't have the technical support staff to monitor things that go late, which means we typically get out at a reasonable time. There's also not much paperwork to catch up on, clients to call, etc. That being said, I do have a lot of studying/reading I do in my off hours but that is just part of the residency program. I also have been coming in on weekends lately for a research project I'm doing, but here all 7 vets (including the director!) split on call shifts so I'm only on call about every 6-7 weeks. Overall, I think lab animal medicine (at least from what I've seen) is one of the most work-life balance friendly specialties around and it did play a minor role in my decision to pursue it. That plus I work with all kinds of different exotic species (turtles to mice to naked mole rats to baboons), I work with scientists rather than the general public (which can have its own challenges), and I get to play a role in maintaining the health and welfare of animals used for research.
If you ever want to chat more about lab animal medicine (or anything really) feel free to shoot me a PM
