Why do casual players seem entitled to cosmetic items added in game?

[AllenThyl]

Agree with that, but there is also the elephant in the room of why a highly-desirable cosmetic item was locked behind savage-level content, particularly when it had absolutely no thematic link to that content.

Because this is a computer game that requires an active subscription, the goal of the company making this product is to get people to spend their time (and therefore money) with this game. It's very much the entertainment value, of doing some game activity, and then getting a reward for it.

It seems probable this was another failed attempt by SE to funnel non-raiders into content they do not like.

No one is forced to do anything, stop sounding like some crazy conspiracy theorist. This is an entertainment product made by a privately owned business, not some government agency which the population is forced to engage with.

By all means, if you or anyone else finds someone demanding savage rewards without doing savage, point me in their direction and I'll laugh at them with you because that's just silly.

Sure thing, here you go:

If it were up to me, fancy glowy weapons and gear would be the only things locked behind savage, tbh.

This whole "but customization shouldn't be locked behind anything" tirade isn't an argument, it's merely your opinion. You simply drew an arbitrary line around certain kinds of items, according to your personal taste.