The fees are generally significantly lower than you'll pay to a...

The fees are generally significantly lower than you'll pay to a services agency (i.e. the agency/business/franchise will take a higher cut than Airtasker does, meaning the actual worker(s) get less). For new or infrequent taskers the fees are on par with similar service marketplaces like Fiverr, and reduce significantly for more frequent taskers (down to 10% for the platinum tier, and I believe it will be a little lower for re-bookings through their new 'Contacts' feature). This is pretty good value IMO for the lead gen, payments processing and insurance coverage. Airtasker can basically be a platform for individual service providers to run their business through.

Another point is that none of these services marketplaces are yet significantly profitable (most, if not all are losing a lot of money), and will require large scale to become profitable, even with the current level of fees. So sure, lower fees would be nice, but there doesn't seem to be a viable business with lower fees, at least not without truly massive scale.