I think the problem with weather is, that it isn't very easy to programm. Especially when the final product should cost less than 100$ (like FSX) I can imagine that there is no money for such programming. And think about it, how many FSX users are unhappy that there aren't windshears compared to the size of user which don't botter?
From the user side (not from the financial side) it would have been the best if they would have included their basic weather as it is now, but let addon developers better plugin into it. Not like AS2012 or similar programs are able now, instead let them replace the weather engine if they wish. If they did this we maybe would have a realistic simulated weather today.
But as said, weather is probably the most diffcult thing to get right in a flight simulator, as in the real world there are so many tiny factors wich can have a huge result onto your plane. As an example, you fly along a open field, at a sunny day in the afternoon, then you come to a line of trees, and you will often feel turbulence created by winds and thermodinamics. To add such a thing in a flight simulator would be probably pretty difficult.
Or another example, in the vally I life we have the most times moderate or little winds, however if you fly out of it you often notice enormous wind speed increases as you leave, which is total logically as the mountains protect from wind. However in a flight simulator such a thing won't be easy to create either, especially when at other days there could be strong winds in the vally as some things changed.
That would cost lot's of money, which only a few people would pay for, as lot's flightsimmers are happy that they have lifted the default trike into the air and never notice any advanced weather feature.
But that's just my oppinion.