1) The cost (direct and opportunity) is ENORMOUS. And even with special federal govt repayment plans, if you don't get that big firm job, the debt will potentially weigh you down well into middle age (with the possibility of a nasty tax bite at the end if you have any assets and the law isn't changed).
2) The likelihood of getting a high paying job is slim. It's even pretty risky from top 10 schools.
3) Even during the boom times, when people from top schools were getting jobs at top BIGLAW firms left and right, people were HATING LIFE at the firm because they didn't realize what it was going to be like. And more broadly, lots of people get all the way through law school and realize they don't wanna be lawyers. This is super common.
4) Non-big-firm opportunities are either super competitive (like govt or public interest), super low paying (also includes lots of govt and public interest), or not a great value proposition (how'd you like 200k in debt to try scratching out 50k a year as a solo?)
Lots of the reasons people want to attend law school are pretty dumb/false (stuff like: like to argue, wanna be prestigious, think its a safe/good-paying career track). The people that should attend law school are those who:
a) won't be financially ruined by the decision,
b) actually want to be a lawyer, and
c) have some real sense of what being a lawyer actually means (e.g. they spent at least a couple years working at a firm in some non-lawyer capacity, or they have a parent who was a lawyer and told them lots about their job, or they spent tons of their time researching law and legal practice. In other words their knowledge of legal practice is not based entirely on fictional TV and movie lawyers).
I'd say that describes under 1% of the people enrolled in law schools nationwide.