Why are they less popular than say Trezor or ColdCard which are more expensive, less convenient and not very beautifully designed?
For example, if you guys were choosing a new wallet now, and came to a shop where all open source hardware wallets are represented, would you purchase an inexpensive convenient beautiful "exotic" wallet? Or would you purchase one of the same wallets you used to consider, like Trezor/Coldcard/Bitbox02 ? Why?
The problem is not the beauty or the design. Open source is important, but that is not all.
An "exotic" hardware wallet for 30 bucks that no one knows might be very insecure.
Ledger may not be fully open source, but it is safe. It is very tested. Many hackers and professionals tried to hack it, but had no success. The same with Trezor and coldcard.
Another point is the group of developers that are working in the device to keep it up to date with the newest security techniques. Ledger and Trezor have a nice budget to accomplish that.
So, it is a good idea to be conservative here. Keep your main funds in a good and tested hardware wallet. Try small funds with exotic ones first.