no, but the tuition is extremely low. ie Uni of Lagos tuition is about $517 usd. there are not unlimited spots in college programs
maybe instead of banning them from leaving, they should have students entering these programs agree to sign contracts that they intend to work in nigeria at least 5 years or they will pay a very high fee since their spot could've gone to a student who planned to stay in nigeria.
students wanting to work abroad can just get education abroad, but it'd cost many times more.