Yup. They know having an electrician do all the work minimizes the risk of you needing to get payed out, so they want it so.
But the insurance doesn't care about your additional cost, since it's your cost, not theirs.
They don't go "cost of professional < additional risk * potential damages", they go "additional risk * potential damages > 0".
Then again, electrical work can be life threatening, so the potential damage is rather high.