Those colleges also do no real research, and offer only a few majors. It does much more social good to donate to an already established university’s facilities, scholarship chairs, etc than it does to create a university from scratch. It’s also far easier to get top professors in an in demand field like some STEM and business fields to agree to come to an established, respected university than one whose future is largely unknown.
Since most R&D heads of major companies aren’t idiots, they recognize that spending $10 million at a decent research university will almost certainly result in a far higher payout to the firm investing $30 million trying to establish a brand new liberal arts college. Additionally, if a major corporate donor to a particular department at a not so well funded school wants to advise the departmental planning committees regarding changes in how undergraduates are educated, most of the time the committee will take these recommendations seriously.
Finally, why should a company care about how low a particular university’s admissions rate is? Unless there was real evidence that prospective CS/ engineering students were actually being denied the opportunity to study the fields because a few top schools are competitive, what sort of sense would it make in establishing another highly competitive school? These companies are well aware that in almost all states with competitive flagships, there are also second tier engineering schools. The only exception I can think of is Georgia, which means there are 49 other states where a good but not great student can study the field he wants to while capitalizing on in state tuition.