There is no mechanism to buy all Doge and the "market cap" of Doge includes lost coins. If you bought all of Doge, its value would be gone since it would be like it didn't exist.
You might as well calculate the market cap of baseball cards.
It's just not the right way to measure the worth of a crypto.
Put another way, if Doge owners decided to collectively sell it would be worth 0.
Hypothetically if some whale wanted to 'buy' Doge say to shut it down or something, they would probably have to spend a lot more than the market cap and as you yourself point out they still wouldn't have bought all the Doge that existed. OP was comparing amounts i.e $8bn seems like peanuts when 'joke' coins are hypothetically worth more than $44bn, and not really comparing market caps (which doesn't really make sense, again as you yourself pointed out).
True, but the flipside is also the case, if someone wanted to sell a significant fraction of a cryptocurrency or high-value stock, they wouldn't necessarily get close to the current market cap either.
You might as well calculate the market cap of baseball cards.
It's just not the right way to measure the worth of a crypto.
Put another way, if Doge owners decided to collectively sell it would be worth 0.