They can and do. By the droves. Great engineers come not only from liberal arts but from a variety of disciplines. The best engineers I've worked with did not have CS or CE degrees and neither do I. Some of them had nothing but a high school diploma or GED. Formal training is certainly not needed, and in many cases, it's a hamper. Also, the money wasted on such is much better spent elsewhere, especially considering the curriculum and many colleges/universities, one that is hardly up to date and does not prepare students for real world development.