Each BTC or ethereum coin have coverage because you need to invest in hardware either asic or mining GPU rigs to produce them ,you need to spent $$$ for electricity so each coin have actual work involved into its production and because of that it has real value.

Instead of this, premined coins are created out of thin air . Developers just decide by the click of enter button how much they want to emit. It can be 10.000 or 10.000.000.000 its their call. You can't do anything about it and as investor you are completely under their control . Your money is under their control as soon as you invest into it. Centralization of anything is always bad because difference of success and destruction is - decision of one or few people. On the other hand, decentralized coins are much more stable because big community of people control them and their future.

Thats why I never invest in coins which are 100% premined / cannot be mined .