Why doesn't water actually perfectly wet glass?

In everyday life glass surfaces are always covered by a layer of, well, crud. Glass surfaces are exceedingly high energy surfaces due to the high density of polar hydroxyl groups and they attract pretty much anything. This means that outside of a colloid science laboratory you will never encounter a clean glass surface.

I spent many years carrying out experiments involving interactions with glass surfaces, and to get the surface clean we had to clean it with chromic acid. A quick Google found instructions for doing this here, but if you ever feel tempted to try this at home do note the comment in that article:

The dichromate should be handled with extreme care because it is a powerful corrosive and carcinogen.

If you survive the cleaning process then you will find a water drop placed on the glass does have an effectively zero contact angle and the drop will spread out almost completely.

But it's only under these extreme conditions that you will see this. Just leaving the glass exposed to the air for a few hours is enough to coat it with a monolayer of whatever organic detritus if floating around (which if humans are present is quite a lot :-). Once this happens you aren't measuring the contact angle on glass, you are measuring it on whatever organic film is coating the glass.

It's because of surface energy

You can just cover glass with a thin layer of material that has low surface energy (like teflon) and then water/stuff won't stick (will stick a lot less) to it...

Check this surface tension article on Toppr for much more information.

To answer the question, yes and no.

The reason why we don't observe water, spread out on its own, on glass, as much as it can, is because of >> see accepted answer :D

However if you spread it yourself, then yea you could make a very thin coat of water covering the whole glass, which could be described as perfect wetting.

For more information: "Wetting", Wikipedia.