I am seeing this behaviour as well and I am not happy with it - and I raised the same question, see here: OH4: rule "when system started" starts, if rules or items became modified
Rich answered:
When you change a .items file, that forces a reload of the rules because when a .items file is reloaded, all the the Items defined by file are destroyed and then created anew which causes a reload of the rule. Otherwise the rule would not pick up the new Items to use as triggers.