You're not that far off. The environment is rapidly changing due to foreign born migrants. There are several paths to clearance.
H1B is only one component of the pipeline. Fun fact: someone with dual citizenship status by descent (India, China, Israel, etc) can also hold a US security clearance if a sponsor wishes to fund the pipeline. Once a person goes through the naturalization process and gets a seat at the table, they always divert funds to the pipeline.
P1: F1 -> OPT -> H1B -> Naturalization -> Clearance
P2: F1 -> OPT -> H1B -> Dual-Citizen Children -> Clearance to Child
P3: F1 -> OPT -> Dual-Citizen Children -> Clearance to Child
P4: F1 -> Dual-Citizen Children -> Clearance to Child
P5: Illegal Migration -> Dual-Citizen Children -> Clearance to Child
P6: Legal Migration -> Dual-Citizen Children -> Clearance to Child
