In Stellar, you must hold a certain amount of XLMs in your account or else you can't perform transactions. What's the monetary rationale behind this requirement? It locks up money in accounts for no good reason. wouldn't it make more sense to compensate the 'miners' of the network with this money?
Accounts, offers and data entries are eventually rows in each node's Postgres DB.
To prevent anyone from creating billions of accounts and unnecessary consuming resources of node operators - base reserve is required as a refundable deposit. It serves the same purpose as fees, but doesn't really cost anything to users.
Current value of base reserve is 0.5 XLM (reduced from 10 XLM on Jan 11 2018), and minimum balance is 2*base_reserve.
I will explain the answer in parts.
make more sense to compensate the 'miners' of the network with this money?
In Stellar there is no concept of miners. In general, there are 2 common ways of validating a transaction on a blockchain network.
PoW and PoS PoW method needs miners to validate transactions. PoS method works on the principle of stake and not miners.
Stellar uses SCP also known as Stellar Consensus Protocol, which doesnt need miners.
certain amount of XLMs in your account or else you can't perform transactions
This essentially prevents people from making a huge number of unnecessary accounts. So the base reserve is set to 1.5 XLM as of now.