That's not really a problem if the supply is continuous. Think of the last time you drank a 12-year scotch, that distillery had to be set up and start producing at least 12 years ago for them to label the product that way but they've continued production constantly since then which ensures there is a steady supply to be delivered to stores.

Spirits are not capital intensive. Building a rocket is very capital intensive. You'd like to be able to reuse it. But if one single mission takes 30 years, then you can reuse this rocket once, at most twice. Let's say you reuse it twice, you amortize the capital cost over a period of 90 years. Now, let's say someone builds the exact same rockets, but they do missions between the asteroid belt and Mars. Each trip takes about 2 years. Everything you can source on Titan, you can find an asteroid to source it from. By the time you reuse a Titan-bound rocket once, you reuse an asteroid-bound rocket many times.