Does anyone know why some D3's dont make there recruits sign national letters of intent and make them verbally committ instead? thanks

There is not a Letter of Intent for D3 schools. The NLI applies to athletic scholarship monies, since D3's do not have athletic scholarships, no NLI.

Some conferences have their own written agreements, valid only inside that conference.

Some schools have a contract between player and the school. Usually referencing grades, conduct, etc.

To add to what BOB has said I have also found that all D-3 schools are not the same with regard to a coach having any say with a player gaining admission--- each school stands on its own two feet