In the early days of pure jets and low bypass turbofans, ingestions were not particularly uncommon (although - thanks to inlet guide vanes - not automatically fatal). There is a pretty dramatic video on a US Navy carrier of a crewman getting ingested into (IIFC) an A-6 and surviving.
In the early days of the high bypass turbofans (where getting ingested is pretty much a guaranteed fatality), ingestions were almost non-existent. I suspect in part because the early widebodies put the inlets higher up, but mainly because people were justifiably scared of getting ingested and so were cautious.
As high bypass turbofans have come to dominate - and with much higher numbers of aircraft, many with the inlets at walking height - a combination of complacency and far more opportunities has combined to make ingestions more common.
Not much we can do about the increase in opportunities (SOP to protect from ingestions are already commonplace - if not always followed), but complacency can and should be addressed.