The only time a third party is successful in a two-party system is when it promises voting reform. If it does not, then a third party has no oxygen to grow out to a full party.

Some two-party nations do have third parties that do not promise voting reform, but we are then thinking Scotland or Quebec where the culture is distinct enough from the main culture that these folks collectively want their own party.

Not so in the USA. There is no separate culture in the US strong enough to bring about a third party. Plus, both parties are so malleable they will say anything to get these voters to vote for them.

Is Voting Reform a good Liberal issue?

It is THE most libertarian ideal to have freedom given to the voters. Voting restrictions such as we have in the uSA should be the enemy of all libertarians. So, why isn't that the case?

Because they are not smart enough to know what bowl they are swimming in. They think that as long as the two big fish don't eat the little fish, then there is no problem. But the problem is the bowl.