The whole point of Agency is to fill in gaps for companies. It had always been the case that you get more money Agency than salary because the work is infrequent and intermittent.
As it has been very busy over the last couple of years, it may have been forgotten that there isnt always work for Agency people. Especially as companies have been taking on so many new people on salary.
Agency people especially have to be good at planning their finances. You have to remember the money you earned this month has to cover you next month as well. Dayrate and Agency always looks like youu get massive pay cheques but people forget it has to cover the non-work time as well.