Do they have sugar or something? My toaster has the bagel setting which cuts down the temperature of the inner electrical elements so that helps. But when toasting, the bagels go from just light brown to over done very quickly.
I thought the bagel setting on a toaster turned on only one side. So the cut side would be toasted and just warms the soft outer crust.
To your question, I haven’t noticed this more with bagels than any other bread-like product.
Bagels are typically higher in sugar content than most breads. The Maillard effect that produces browning works on sugars. It can be more pronounced if you have a bagel with fruit added to the dough during preparation.
Bagels typically have a lower water content than most breads. Water has a high specific heat and absorbs quite a bit of energy to heat up. The difference is small but the result is the surface temp of the bagel increases a bit faster for exposure to the same heat source.