So my guess is they think it's a joke. But if they think it's a joke, they'll have to put their mouth where their money is, which means they will have to dump legacy for 148 coins, risking being left on the wrong chain that reorgs and disappears if UASF gains traction. Let's see.
But it also works in the other direction. This is the fundamental problem also of PoW change propositions.
At a certain point, you need to dump your original bitcoins. That takes a lot of balls, and you might as well make the wrong move. So thinking that the big whales are going to dump the original chain for any new chain, is a dangerous bet - especially if they want to rip off one another too in this game.
The smartest move is to keep your double coins, and wait until the dust settles. But if everybody does that, you get an even value split of the market cap.
The 148 chain can't reorg, so it's not a total wipeout risk scenario. Sure if 148 doesn't pick up traction, you can end up with a coin that crashes hard, but notice how even useless bitcoin unlimited tokens in bitfinex still have a price, so you could dump them for cheap and still get some out of it.
On the other hand legacy can reorg which means you end up with literally 0.
So legacy is under this constant pressure of a potential snowball effect happening on 148.
It takes only like 20% hashrate on 148 and the rest of miners should start getting very nervous.
Notice how if Core allows 148 support, bitfury said they will mine it.