1. Block Size Limit: Each Bitcoin block has a maximum size of 1 megabyte (MB). This limit was set in the early days of Bitcoin to prevent the blockchain from growing too large and becoming unwieldy. However, it also limits the number of transactions that can fit in a single block.

2. Transaction Data Size: Each transaction also has a data size, which includes information like the sender and receiver addresses, the amount of Bitcoin being transferred, and the transaction fee. The average transaction size is currently around 229 bytes.

3. Difficulty Adjustment: To maintain a consistent block time of around 10 minutes, the difficulty of mining Bitcoin is automatically adjusted based on the total hash rate of the network. When more miners are competing to solve the block puzzle, the difficulty increases, making it harder and taking longer to find a valid block. Conversely, when there are fewer miners, the difficulty decreases.

4. Mempool and Transaction Fees: Not all transactions are immediately included in a block. They first enter a queue called the mempool, where they wait to be picked up by miners. Miners prioritize transactions with higher fees, as that's how they earn their reward. This means that transactions with lower fees may have to wait longer to be confirmed, and some may even be dropped from the mempool if they sit there for too long.

So, while 600 seconds might seem like a lot of time to process transactions, the block size limit, transaction data size, difficulty adjustment, and mempool dynamics all contribute to the actual number of transactions that can be included in a block being lower than that theoretical maximum.

Here are some additional things to keep in mind: