Why do you need to remove your contacts before getting in the tanning bed?

As long as the eyes are kept closed and protective eyewear worn, the UV light cannot reach the eye or lens, so there is no reason why you can not safely wear your contact lenses while tanning. However, just as you should moisturize skin after tanning, contact lens wearers may want to use eye drops to combat the drying effects of the lamp's heat.

http://www.hometanningbed.biz/tanninghealth.html

Problems have developed in the past with contacts sticking to the eyes while tanning. The primary reason is due to de-moisturization. Your whole body naturally loses some moisture during the tanning process, including your eyes. If someone is going to tan with their contacts in, it is recommended they not only wear protective eyewear, they should also use moisturizing drops prior to or just after the tanning session to prevent any discomfort.

http://www.wolfftanning.com/faq.cfm

The heat could melt them.

Interesting question... Wow, they melt lol

Because they will probably dry up and get stuck to your eyeball.

they heat up!