The foremost reason is to simplify the invoice process, since the user costs of the platform will now solely be charged to client. The €1,- in user costs you used to pay, will now be paid by the client. This means that the client will now be charged €3,- instead of the previous €2,- and the cost of the freelancer will change from €1,- to €0,-.
In the end this changes practically nothing, the client will continue to pay equally as much as they used to and the freelancer also earns exactly the same as before.
Example: Where you used work a shift for €16,- and ended up seeing €17,- on your invoice being charged before the user costs were deducted, you will now no longer see any user costs on the invoice. In this case you will see on your invoice the same price as on the platform.