You'll get many different responses to this question depending on who you ask. If you want to read into further i recommend you read the great scaling debate[1]. Its pretty long but does a fantastic job of summarizing the history.

In short the most popular reason for not having a block size increase (to allow many low fee transactions) was that it would increase the cost of running a full node, in turn centralising the network. More transactions would mean nodes would need a bigger hard drive and a better cpu to process the transactions. The small block camp wanted people to be able to run nodes on a raspberry pi. This theory is misguided in my opinion though, they chose to sacrifice cheap transactions to keep node running costs cheap.

[1]https://medium.com/hackernoon/the-great-bitcoin-scaling-deba...