Why does T-Mobile use DoD network space (21.0.0.0/8) for it's internal network?

I recently fired up an LTE router using a T-Mobile SIM. Within an hour I had two different WAN IPs that belong to AS749 DOD NIC (in 33.79.135.0/24 & 21.140.100.0/24).

Again, those were my WAN IPs. My public IPs were in T-Mobile's AS21928 network space.

And for clarity, T-Mobile likes using DoD IPs for it's internal routing. It's safe as long as DoD never starts advertising it's IPs as publicly routable. And if DoD does... beats me.

Not really related: The DoD consolidated it's addresses into the previously unused AS749 in 2021, after a weird dead FL company started publicly advertising DoD addresses within it's own ASN.

    The move evokes the 2021 mystery surrounding AS8003,
    an ASN associated with a defunct Florida company that
    started announcing all of the formerly unused IPv4
    address space belonging to the US Department of Defense. 

    Later that year, the DoD quietly moved the address space 
    to a formerly unused ASN, AS749, which continues to 
    announce more IPv4 address space than anything else in 
    the history of the internet.

ref: https://www.kentik.com/analysis/aws-announces-super-aggregat...

dead fl biz ref: https://www.kentik.com/blog/the-mystery-of-as8003/