Shouldn't we talk about multigrade detergent oil loosening the sludge in the trap?
No becaue they don't
This is another urban myth.
A detergent oil is not a washing up detergent, It does not clean baked on / packed in deposits from your engine except in TV commercials made by people with qualification in phycology & mass marketing, not SCIENCE & ENGINEERING..
At one end of the detergent molecule is a radical that hates itself so will bond to anything other than another detergent molecule.
At the other end the molecule will only stick to an oil molecule
Thus when they come across a lump of crud, one end sticks to it.
Eventually the bit of crud will be totally surrounded by detergent molecules so will be a lot bigger and easier to filter off.
The reason why you don't use high detergent oil in bikes with out oil filters is the little bits of crud surrounded by oil molecules do not settle out and continually circulate around your engine slowly erroding all the oil ways .
It will not scour your engine like a dish washer
Sludging oils were similar except both ends of the detergent molecule are homophobic so each end sticks to a piece of crud and neither end wants to hang around with those greasy oil molecules.
Thus they sort of glue all the bits of crud together into really big globs so when they get into the oil tank they will sink to the bottom below the outlet and stay there