It is cheap because supply is infinite and there is no mined scarcity premium. Natural diamonds are artificially kept expensive by De Beers-style supply control. Moissanite is a manufactured crystal produced in bulk. The 'catch' is not quality, it is simply that there is no prestige premium attached.
Moissanite is about as ethical as it gets. It is lab-grown silicon carbide, no mining, no child labor concerns, minimal environmental impact. The energy use is real but tiny compared to diamond mining. For ethical buyers it is one of the cleanest options.
I listed mine on eBay after 4 years and sold it for about 25 percent of what I paid. That is actually better than I expected. Treat it as 100 percent depreciation and you will not be disappointed.
One thing nobody tells you: moissanite can get a hazy look if you use an ultrasonic cleaner on a poor-quality stone. Stick to warm soapy water and you will be fine.