One of the technical problems with directory mappings in snaps is that a directory has to exist in order for you to mount to it, and snaps use a read-only filesystem so can't mount to a directory not already pre-created in snaps. However you can connect /home and /media if you connect the relevant permission (but not /root).
It is definitely a source of general frustration, and I think largely because people are still often using it for CLI tools rather than GUI tools which can make use of portals to grant file access permission and/or use an arbitrary path more easily - which is how it works so seamlessly on macOS [and is supported by flatpak/snap for GTK3 at least].
(Disclaimer: I work at Canonical/Ubuntu in the Support organisation. But not directly with/on snaps, this is a user perspective.)
It is definitely a source of general frustration, and I think largely because people are still often using it for CLI tools rather than GUI tools which can make use of portals to grant file access permission and/or use an arbitrary path more easily - which is how it works so seamlessly on macOS [and is supported by flatpak/snap for GTK3 at least].
(Disclaimer: I work at Canonical/Ubuntu in the Support organisation. But not directly with/on snaps, this is a user perspective.)