Hand carrying it poses risks as well, like risk from a natural disaster. The goal is to have a geographic separation beyond an hours drive.
That's what you pay Iron Mountain for. They have vaults that can withstand just about anything you throw at it. Short of a nuke going off in the city, then you have other problems to worry about than where your backups are.
Sneakernet throughput is insane compared to most affordable pipes. It takes about 2 hours to go through a tape straight stream. LTO7 holds 6TB/12TB. Even factoring in the transport time of ~4 hours after pickup and 1 hour to put it in a box, you are looking at ~550Mbps with full 2:1 compression. I can sustain that speed from two of my DCs, but hell if I want to send it across to London or Singapore.
Let's not forget about the fact that you are stuffing the pipe with all that traffic. I doubt most SMBs have even the ability to get a 10Gbps pipe I got. My 10Gbps pipe is not dedicated to our DR product, but all traffic. So even if I was replicating 6TB every 6 hours, I have plenty of room to allow others to do things. With most SMBs, they could hope for a 20Mbps up, but most are running on commodity turd pipes with shittastic peering which slows them down.
Of course, this all predicates on what exactly you are backing up. I have 4PB in one DC alone. Tape makes sense. Most SMBs, once their digital packrat tendencies has been culled, don't have even enough to fill up an LTO4 tape.
Cloud backup for small datasets, tape for large.