Seasons serve a dual purpose. The first is to give you a vehicle for starting fresh but also provides the benefit of carrying your items/gold/xp over to the remainder of your account. The second is to add a layer of competition to individuals for those that want to participate. Granted, streamers will almost always be at the top because of the time they commit to the game (or in some cases, the exploits they leverage).
I have no problem with introducing new legendary items to seasons as an incentive for people to play them, as long as they continue to drop them into non-season. I think Blizzard is doing a good job with improving the catalog of legendaries and benefits provided. I would prefer to stop seeing sets be the driving force to build changing mechanics, but it's easier to balance around sets and provide complimentary items then balance around individual affixes. This method also lets them spend time on new maps, expansions, and additions to the game (such as Kadala).
In the end, you aren't forced to play seasons, just like you are not forced to play hardcore. It always confuses me to see comments like this when they pop-up.