Blockchain is a piece of technology based on Digital Ledger Technology (DLT) that maintains a public ledger of transactions. This sounds like to be only suited to financial transactions, but blockchain can be introduced to any field even with the only motive to make a process more efficient.
The primary reason to choose blockchain to implement love locks was the ‘foreverness’ that a lock could achieve by being implemented on the blockchain. Every lock that would be put on blockchain would leave its trace forever. This is far better and more promising than locking a padlock on a bridge where the lock could be removed by local authorities at any point in time introducing an abrupt end to your symbol of an unbreakable love.
Similar implementation could be done on a centrally controlled environment as well, but that would not have guaranteed the foreverness that blockchain technology can provide to a transaction (locking a love lock in this scenario).