Of course your team knows what your product does. But do they know why they're building the specific features that they're building?
You can get good results for a little while by hiring smart people who want to build cool stuff with new tech. If you want your team to stick it out through all the less fun maintenance tasks and technology upgrades that come with a long-term product, then the team needs to be invested in more than just the technology. They need to believe in what you're building, and they need to know the reasoning behind the particular features that have been prioritized.
If you want developers to stick with you for the long term, demonstrate trust. You'll be amazed what that trust yields in return. You don't need to clue your team in to every marketing and business decision that happens. But make sure that at the start of each new milestone, you make it clear how the large-scale deliverable fits into the product strategy, and how the developers are contributing materially to the success of the company. With the big picture, developers will use good judgement when they're forced to make decisions that will have long-term effects, such as architectural choices or judgement calls about technical debt.
You need to retain your talent, especially as your company grows. Developers who are invested in larger initiatives and recognize their strategic value will be more likely to stay on and grow with you.