Yup, but no incentive. They are literally making millions of dollars for a fraction of a penny in CPU time to sign a cert. Why offer the same thing for free? Try to sell it as more secure and trick lots of people...
who ever said free? they could make a paid service like LE with automated renewals etc that integrates better with enterprise software, or that does better audit logging, or any number of things. let’s encrypt is a great service, but there’s still plenty of money to be made off overzealous corporate security policies