The two major reasons are the cost of online access and the terms or conditions demanded in license agreements. Still other publishers offer individuals and libraries the option of subscribing to either the online or printed version for approximately the same price. A commitment to archiving is an expensive proposition, as electronic data is even more fragile than print on paper. In addition, as technologies change, electronic data will need to be migrated from one system to the next in order to be accessible. Were HSL to pay additional fees for duplicative online access to some journals, the acquisitions budget is so tight that we would have to cancel access to unique titles in the collection.
Many publishers provide free trials or even free global access to their journals.
In the print environment, libraries purchase and thus own books and journals. In the online environment, the acquisitions model is very different. However, if there is any break in the renewal of the online subscription, then in addition to paying for current issues, the library must purchase access to backfile content at the then-current rate. Paid journals usually require that libraries formally agree to a set of terms or conditions for use. Thus access would be limited to specific areas or departments of a campus and be unavailable from others.