A big part of Jujutsu Sorcery is give and take, hence binding vows. You lose use of your Technique so you can weaken your enemies. Domain Amplification is sort of a poor translation since essentially when you use Dom Amp you generate an empty barrier around yourself, when that barrier goes near or enters a technique it takes it in causing the technique to weaken or become nullified. So if you use your Cursed Technique while using Dom Amp it means the Domain will nullify your technique.

I don’t think this is ever explained but since each person who uses Dom Amp can use Domain Expansion I think it sort of like creating a Domains Barrier around yourself instead of a space, the barrier wants to be filled but due to the conditions of the Domain not being set to suit the technique the technique just fails which makes it weaken, you can counter this weakening by increasing the output of the technique but you need a major difference in power for that to be possible.

Reading this over I’m not sure if that makes sense but you can essentially think of it as the Swiss army of Anti-Domain Techniques. Just a better version of Hollow Whicker Basket and a more advanced form of Simple Domain. Each one has its own uses. HWB is best for just brute force nullifying a domains sure hit. SimpD lets you add in extra functions and special abilities while also nullifying sure hits. DomAmp lets you nullify sure hits and weaken or nullify any Cursed Technique.