Yeah, they do. But not nearly enough to warrant their valuations. The companies are fine and won´t go under in a crash, but the multiples are a debt the creditors won´t be able to recover in full, unless they wait decades once the prices go into correction.
Whoever buys after the next market crash - whenever that comes - will get real value for their money. Right now people are just speculating that there will always be another buyer, to whom they can sell the debt. Just like the banks did in 2008.