We took this question off of the frequently asked items on Google and used it verbatim for the title of this blog post because within the question itself, lies the answer!
Moissanite is so cheap because it is NOT a diamond!
The diamond industry itself is still standing on the false ideation that diamonds are rare, and because of that... their pricing is insanely high. They have spent the last 80 years trying to portray these stones as items that retain their value over time and because of that, I don't forsee their pricing getting much cheaper any time soon.
Lab Grown Diamonds have put the whole industry into a tail-spin because there is no false narrative surrounding them. The same thing applies when it comes to Moissanite which is also a lab-grown gemstone, only add the fact that they are not a diamond to the mix and voila! They are even MORE affordable :)
At the end of the day though.... a Moissanite will never be a diamond and so as the prices of Lab Diamonds continues to fluctuate, the choice between the two over time... will become less and less about the price and more about what is going to make you the happiest for your buck!