Betazed is a pretty quiet place and can actually be pretty unsettling for non-telepaths. Actual speech has become something of a vestigial thing so much so that individuals like Deanna and Lon Suder are considered to be disabled by the general population, and frequently need special accommodations to fit in. That’s why parties and ceremonies often feature repeating sounds - there’s no extraneous speech to get in the way of the tone as it spirals through the air. Because of this, Betazed is a mecca for the instrumental arts, and concert halls and parks are the most enjoyed form of entertainment.
Lwaxana Troi is so loud and bombastic in her speech because she tries to convey what the Betazoid thoughtscape is like. It’s big and expansive and emotional and she uses her speech the exact same way because she wanted her children to experience that for themselves despite their hybrid physiology. There is no filter that Betazoids employ in their thoughts to each other. That sort of naked honesty is something valued and appreciated most by their communicative culture, and it’s something that also comes out in their weddings.