Some schools can't afford to hire a teacher for AP courses, especially if there are not enough interested students. However, students who are interested can enroll in an online course.
For schools that can't offer more than one or two AP courses, or for home-schooled students, online AP courses make more topics available to students.
The more students in a school who develop interest in online AP courses, the more incentive a school has to start its own AP course program.
The College Board audits online courses in the same way it does with physical school programs, through the AP Course Audit. Accredited schools are listed in the AP Course Ledger on the College Board's website.
California, Florida, Iowa, Kentucky and New Mexico offer grants to help schools get students access to online AP courses. You can contact your area's Regional Office of the College Board for more information.