"Wrapped Bitcoin" is not "porting" BTC to Ethereum. It's merely a token that represents some sort of claim on actual BTC held with a single custodian (Bitgo).
And there are wrapped BTC tokens on Ethereum that utilize cryptoeconomic incentives instead of the reputation of a custodian to guarantee redeemability for BTC: renBTC and tBTC.
WBTC was just the first to launch so has the largest market cap. It's also possible that WBTC's reliance on a trusted third party is perceived as less risky than reliance on novel cryptoeconomic incentive schemes.