Criminal law does not necessarily pay less, though it often does. Think about the fees which will be paid to the guys defending the CHC officers. Or the lawyers representing each
PAP minister in the numerous defamation suits over the years. Or Susan Lim's lawyers. When the litigant employing a criminal lawyer has deep pockets, the fees will invariably reflect this.
However, in small practice criminal law - your client is either:
(1) a rioting Bangla worker
(2) a Filipino maid who has snapped and killed/attacker her employer
(3) a distraught housewife who has been abused by her alcoholic, unemployed husband
or some other variation of the above. A class of persons who deserve legal representation, but can't quite afford it. Who will pick up and foot your invoice at the end of the day? And even if they can and do pay, where is your next file/case coming from?
On the contrary, in corporate and finance work your clients are banks or powerful multinationals which have the budget to pay hefty legal fees. The workflow is continuous, repetitive and pretty much guaranteed once the relationship is there. Corporate and finance work is a far better money spinner.