Contacted BLM in Butte several years ago their main reason for not online reservations was POOR internet service, I'm thinking that was an excuse. BLM Montana website has been down for a long time to contact them, don't beleive me check it out for yourself!
I agree with what they said there really I no need for it and Montana is a fee yrs behind the times with other states
This is probably a question better suited for the BLM than random internet people. My best guess is that they don't have the money or a particular need for it. An online reservation system, or any reservation system, requires a lot of overhead, which they are probably not able to provide.
Thanks! Your answer is awaiting moderation.