Why do wheel covers even exist if they can cause so much damage?

Bit of rant here, but:
Was driving on M1 today, there was two cars in front of me, 1 was avensis taxi driver in front of me, and in front of him was some taxi van too. Out of sudden I see sharp plastic pieces and metal bits flying all around. From what I understood the wheel cover fell off the van and the taxi in front of shattered it to pieces with his windshield or bumper then all parts went flying onto me and across motorway. What kind of (no offense to anyone) - Idiot uses wheel covers without some kind of zip/cable ties used to restrain them to actual wheel. I am pretty sure one of those pieces could easily pierce tire or so, or if it was a motorcyclist or someone with roof top open (I know weather is ****, but in general).

I don't get it, whats the point of these covers? everyone knows there is a standard black metal rims under it.