Most titles in this database was purchased by the LSC Libraries (not just UP). Access depends on how many copies were purchased and/or how many uses each title is licensed for, which is set by the publishers.
Some books are part of a DDA (demand-driven acquisition) program.
The last piece of metadata on the book's "detailed record" page will tell you the "concurrent user level," whatever it may be (from limited access, 1 user all the way through unlimited user access).
The "Publisher Permissions" line just above will let you know how many total pages you're allowed to download and print.