Likely was easier for all involved.
When conditions permit.
For anyone else curious, per AI and sourced to Time magazine...
“Overview of 21 Air and Amazon PartnershipPartnership
Start: North Carolina-based and Miami-headquartered cargo carrier 21 Air began operating Boeing 767-300 freighters on behalf of Amazon Air in late 2024.
Fleet Share: 21 Air operates a small fraction (around 8 planes) of Amazon’s broader cargo network, which utilizes over 100 aircraft through various third-party contractors.”