There are several articles that outline the benefits of taping a hockey stick. Check out this article and this one from livestrong.com. I am posting below some excerpts from the former article to cover the benefits of taping a hockey stick.
Surface Protection
Wood splinters, especially when it is worn away by consistent friction with the puck. By taping the wood blades of their hockey sticks, players protect the surface and edges from breakage, extending the life of their equipment.
Moisture Repellant
Moisture infiltrates wood and it can cause the material to warp. Hitting a puck with a bent-out-of-shape blade is as effective as playing ice hockey in your flip-flops. The porous wood absorbs the moisture from the ice rink unless it is sealed. Players use tape on their blades as a moisture repellant.
Puck Control
On the website ESPN the Magazine, retired professional ice hockey player Brian Rolston says that modern fiberglass hockey-stick blades are slippery and they do not make good contact with the puck. He says that wrapping them in hockey tape helps the player direct the puck and shoot it where it needs to go. Another ice hockey retiree, Bobby Nystrom, adds that when a player receives a pass, the tape around his blade cushions the hit, keeping the puck from bouncing off.
Regarding your opinion that manufacturers should provide such material coating on their products to avoid the need for taping, the main problem is friction. After a few uses, whatever material is coated will start to wear off. Rather than having a partly worn off coating on a stick, it's better to use inexpensive tape before each game to ensure a consistent level of control and discard it after use.
