But what if millions of people tries to do the same? You think that Bitcoin or Ethereum network will be able to process it?
Through Bitcoin layer 2 and layer 3 solutions, yes.
As for WBTC, I'm just saying that it's funny that more Bitcoin is locked up in the Ethereum network than there is BTC on the Lightning network. Plus, article says that there is only 1000 BTC in the LN! That's saying how low adoption of the Lightning network is...
Though Lightning's adoption is no doubt very slow, it's really expected for there to be more bitcoin "on" Ethereum though. Lightning is for small transactions, whereas WBTC are mostly for staking. It's pretty much spending(LN) vs hodling(WBTC) for interest and for those "DeFi contracts", so of course there would be more bitcoin locked up on Ethereum.