A big part of the issue of staffing levels is automation. Examples here of FR and BA in LHR. More automation at check-in/bag drop means less staff required and bigger cost savings. It's unlikely many of those check-in staff would be ticketing trained for FR and even BA, but they are still people that can offer assistance and advice, and be a face for the Airline. I can't imagine FR would be paying handling agents for an abundance of ticketing agents that would only really be needed in situations like this. Usually 1 or 2 people manage these desks on a daily basis.
Labour savings are great, until it goes wrong in these situations.
Secondly many Airlines are outsourcing their ticketing (this is reference to full service Airlines, not EZY and FR that tend to still have ticket desk presence at most Airports)
With a more "remote" style of ticketing, Airlines don't have the people on the ground with the expertise. I've seen this in action and a lot of the time it works and is more efficient. A person at the end of a phone or behind a computer screen not even near passengers can rebook a whole flight in a fraction of the time, mainly because they haven't got someone stood in front of them wanting all the options, arguing, chatting and basically distracting.