When I went to study law, I had no idea what kind of law exactly I wanted to practice. However, I was lucky enough to get a taste of public, family and commercial law whilst still at uni and I simply found the latter most interesting, challenging, rewarding and suitable to my personality. Also, improving on my commercial awareness quickly became more than a chore - I simply got quite passionate about it over the years. The two years of in-house legal experience that I have under my belt only cemented my decision to work toward qualifying as a commercial lawyer. In essence, I think that having actual experience really helps in realising if you like what this job entails or not.
I would also like to echo what others said above about stability - of course, in the present times nothing seems to be "strong and stable", especially for our generation, however a career in commercial law is still largely deemed to be able to provide one with some sense of security, not least financially.
Speaking of salary - I confess it used to be one of my major considerations, but not anymore. When I was a poor EU student who had to skip parties with friends because I simply could not afford going to them, the allure of a six figures salary offered by some legal tycoons was very thrilling. Interestingly, this has changed as I grew up. Surely, I would like to earn decent money, but working in-house, I learned to value and appreciate good work-life balance and peaceful working environment over big bucks. Thus my decision to train in-house - I guess I got to the point in my life when I want to start a family in the next few years and I would actually like to see my kid(s) growing up (look at me getting suddenly mature and all).