I've answered multiple people with this same question. I can divert you to this thread that I answered:
In summary, there is not a true reason for people to get a discount for X-Plane 11 just because they own X-Plane 10. It makes no sense. People who owned X-Plane 9 paid full price for X-Plane 10. On top of this, X-Plane 10 came out years ago (2011 or 2012, I think). Some people, such as myself, owned X-Plane 10 in its early days. We got our money's worth, and then some... many of use spending more money on add-ons than we actually did for the simulator itself. X-Plane 11 is a NEW release. Not an update. I hope you understand that while Laminar Research strives to make a quality product, they are also a business. If they were handing out discounts to practically everybody (as you suppose), how can they make a sufficient profit? X-Plane 11 has been years in the making, and brings a lot of new things to the table. There is no reason to get a discount UNLESS you purchased X-Plane 10 within the last two or three months.
When new console games come out, people are always happy to purchase the new versions (such as Madden or Fifa), even though they are not much different than the previous version. And those are $60 each. X-Plane 11 is a leap from X-Plane 10, with MANY new features and enhancements, and required considerable work, time, and effort. I am a loyal supporter of X-Plane and am happy to pay for Version 11. :-)
*I am not affiliated with Laminar Research.