BTC and ETH have their respective technology and that's why they're considered at the beginning by many. Although being the first one really portrays a big part.
But, look at those projects after bitcoin was launched. There were many of them that can be said that they're one of the first projects after bitcoin but they're nowhere to be found today and they didn't survive.
That's why the technology of the project is still having that big share of its pie and why investors are choosing them. There's also this consideration that some of them really have a good proposal of their technology but didn't gained a lot of attention because of lack for marketing and spread of its word.
most projects that come after btc are crap. that's the main reason why they did not survive. their respective devs are just here to fill their pockets. only few projects have the sincerity to deploy their technology and make a change in this market. as we have seen, a lot of alts disappeared already because their foundation itself is weak. you will know if the network is valuable if it is being used by many projects like eth.
I agree, those developers that are for the money. They see themselves very short term with the project that they have been developing but those that have been looking at their project being used by the people and with actual technology that it promotes, they are rewarded for working on it for a long time and perfect example is Vitalik. Too many alts were already out of the market after bitcoin and even they were made before the popular projects these days, we can learn on one fact that bitcoin has saw all of them.