[wgj]

You can cellar your own wine. Lots of people do it, but cellar conditions matter and it's an expensive hobby. It's nice to not need to know five years in advance what you will feel like drinking tonight. Optionality is worth something.

But yes, with care a hobbyist can do better than how some retail wine is kept.

Edit: The main points are 1) cool (~55F/13C), 2) dark, 3) not too dry (70% humidity is usually recommended. This is to protect the cork), and 4) store on its side, also to protect the cork from drying out. Five years is a long time.

Most retail wines are made to drink now though. If it's on the shelf it's ready.