I'm not really sure why, but I do know that if they had, library books would not be "infinite" on the Libre as (I believe) they currently are. (I haven't actually borrowed any myself due to my library not offering any this year...
)
Also, I have noticed that the "power off" option doesn't seem to be very accurate. (Set to 30 mins, often turns off after about 20 mins) That may indicate that it doesn't have a very good internal clock.