Imagine you're starting your own country. You're going to need laws to govern your people. There's infinite ways to structure your country, but however you choose to do it will be written in code.
The code for your laws is one or more smart contracts deployed to a blockchain.
With me so far?
You're probably not going to get your laws just right the first time. You'll need to upgrade the code at least once if not multiple times over the next tens to hundreds of years. If you start a good enough country, it should outlive you.
You could start a monarchy or an oligarchy, but that's not a very good country. No one wants to be a citizen under these systems unless they can be part of the ruling class. At best, someone will copy your good ideas and start a new democratic country.
So, if you want to attract citizens and build something that can outlive you, you have two options: DAOs and non-upgradeable contracts.
DAOs are a lot of work. You have to create a token contract, a governance contract, and authorization code for each of your other contracts. Then you need to distribute your token via an ICO, mining event, or some other mechanism. And finally, you need to coordinate all your citizens' effort and proposals to improve the "country." This is multiple full time jobs. In time, a DAO can run itself without the original founders, but you have to care for it in the early days.
Non-upgradeable contracts are dead simple. There's no governance at all. Citizens can join your country without worrying about the laws changing. If you or anyone else decides an upgrade is needed, you just make a copy of the country's original laws with whatever modifications you want. Then you start a new country. Not everyone will follow to the new version, but that's ok. This is all about freedom anyway.
P.S. Non-upgradeable contracts typically have a centralized front end. If you own the website, you can point it at whichever version of the contract you want. This way, "immigration" into the new country is the default for the average citizen.
P.P.S. Non-upgradeable contracts may not be the best choice for contracts that hold deposits (like staking pools, ICO treasuries, etc.). In case of an exploit in the code, you should really have a way to patch the hole and return everyone's money. DAOs aren't perfect either in the event of buggy code, but upgrades give you more options on how to move forward.