> A third of them were made redundant.

More like something closer to 100%. The ATM was notable for enabling a complete change in mission. The historical job of teller largely disappeared, but a brand new job never done before was created in its wake. That is why there was little change in the number of people employed.

> because of deregulation and a booming economy and whatever else.

The deregulation largely happened in the 1970s, while you're talking about 1988 onward. The reality is that ATM actually was the primary catalyst for the specific branch expansion you are talking about. Like above, the ATM made the job of teller redundant, but it introduced a brand new job. A job that was most effective when the workers were closer to the customer, hence why workers were relocated.