Blockchain is a register book.
This book consists of several pages and each page records multiple transactions there. As soon as a page has been filled up, it takes time to enter the registry, and then you can write other transactions on the next page.
Before a block is entered into the chain, it must go through a verification process to ensure that everything written in it is correct and true. This process takes about 10 minutes (for Bitcoin Blockchain) per page.
This whole process makes bitcoin's transaction processing time longer.