Why does one need to cancel tickets and pay penalties for new tickets

I had mistakenly booked tickets in my girlfriends nickname and needed the name to be changed on the ticket , ticket where most unhelpful and said they would need to cancel the tickets and reissue new ones. I contacted Mango Airlines direct and got the ticket changed online for a cost of R220 I also contacted Kulala Airlines and was advised that had I bought tickets directly from them I would be able to do a name change for free . Why are the travel agents *********** clients , this is my first and last time using travelstart my girlfriends company used them in the past but this will also end