I found this:
The problem here seems to be her former label, Blackground Records. The label is now defunct, but before going under, they sold hundreds of hit songs from their archives to Reservoir Media Management, including the majority of Aaliyah's catalog (her first album was not included).
Aaliyah's albums are among many other Blackground releases that are currently unavailable, including:
Aaliyah - Aaliyah
Aaliyah - One in a Million
Romeo Must Die Original Soundtrack
Ashley Parker Angel - Soundtrack to you Life
Toni Braxton - Libra
Tank - Force of Nature
Tank - One Man
Tank - Sex, Love & Pain
Timbaland & Magoo - Welcome to Our World
Timbaland & Magoo - Indecent Proposal
Timbaland & Magoo - Under Construction Pt. II
Of all the artists on the label, the only big seller whose albums are available online is Jojo, and she is currently is suing Blackground for not releasing her third album. [Suing For Her Freedom]
Reservoir will probably release these albums eventually (and make tons of money off them), but it seems like they're in no rush to do so.
https://www.quora.com/Why-isnt-Aaliyahs-third-and-final-album-available-for-streaming-or-purchase-anywhere