Why can we not upgrade the software product Global Mapper to a new version after a certain time?

A perpetual license for Global Mapper (as of version 14) comes with an upgrade right to a new version that lasts for one (1) year. After that period, an upgrade needs to be purchased separately.

Source: https://www.bluemarblegeo.com/support/licensing-policy.php (retrieved 2017-07-26)