Some students may get all of the information that they need from the web site, an informal visit, and/or talking to the college fair rep without getting recorded, perhaps because they do not know that they have to “show interest”. Also, Tulane offers both EA and SCEA, where SCEA is the way to “show interest”. In general, why would regular EA (as opposed to SCEA or ED) be any kind of way of showing interest beyond RD, since applying to as many of one’s schools as possible EA is a strategy to try to net an early safety?
UMass - Amherst also considers “level of applicant’s interest”, so a highly qualified student who realizes that his/her perfectly good state flagship may not be a true safety because of that factor may choose to add additional schools to his/her application list “just in case” – the opposite of what you want to see.