Nothing is an incentive to convert BTC to any altcoin. That's like stabbing yourself in the foot. I'd rather want an direct fiat option to buy GB.
This statement has no actual basis in fact. Yes BTC came first. Yes it's the current market leader. Yes it's the closest to being considered an actual currency.
However we're dealing in technology here. It's highly likely that many "alts" will outperform BTC from this point forward. Many smart people intend to profit in this way.