Trusted by whom? Altcoins are trusted by (at least part of) their supporters as well. The main difference compared to Bitcoin is the much smaller number of people that trust in these altcoins.

It is correct that altcoins are generally viewed with more skepticism, because there have been a large number of premine and other scams related to them. However there are also serious contenders among them. The reason that even these coins fail to gain prominence is not related to trust issues. The primary reason is that Bitcoin is simply too dominant to allow for the existence of equally important altcoins. The network effect of Bitcoin as a first mover draws in all resources in terms of developer talent, liquidity, and market acceptance. Even for perfectly sincere new altcoins it is extremely difficult to withstand this effect and grow longer term.

ya.ya.yo!