Why do I feel like it’s so hard to quit IB? [2nd YR @ BB M&A] - do you hate IB or just working in general?

Depends on what you value. Even if you hate working in general, you will spend less time at work in most other roles. Personally, I couldn’t stand always being on call/glued to emails for pointless fire-drills. Even when I work 60-70 hours per week in my current role when things get busy, I at least know I have the freedom to completely disconnect on the weekend. If you value risk-averse, immediate high earnings potential, there are practically no fields, if any, that are better than IB, especially when considering you can break in with only an undergrad degree and can make it to the highest level of seniority without having to get an advanced degree. If you value autonomy over your schedule, there are very few fields worse than IB. Again, it all depends on how you look at it, and your value system is going to be the main driver of whether or not you’ll view the sacrifices you have to make in the field to be worth it.

Also, when considering other careers, be realistic in terms of where you could be successful given your skills and options. I loathe when people compare IB to something like medicine, because these fields are not apples to oranges, they provide value in different ways, require different levels of credentials/education, and these are not two roles you can “hop between”. Likewise, don’t let a jaded VP suck you into the mentality that you should never be uncomfortable with the hours or demands of the field because some people on an assembly work long hours as well; yes, it is important to practice humility and gratitude, but once again, it’s not a fair comparison - if you had the skillset/credentials to land a role in IB, your “backup” gig would not be a McDonald’s shift manager.

Work in IB is simply not fulfilling at the junior (and arguably senior) levels. Yes, it's probably the best risk-adjusted career for maximizing cash compensation, but thinking about grinding for the next 5-10 years to make VP/MD/partner/etc. is not appealing to me at all. 

I personally came into IB thinking I'd do the 2 years EB -> 2 years MF -> greatness path but have already cancelled on those plans. Exiting to a startup in a field I find really interesting after bonus instead.