It's all part of the "loudness wars" (google for more info! ........ Which affect tv sound, amongst other things.
I'm not sure WHICH COUNTRY the original post comes from! However, if in USA, there are "tv loudness control" gadgets you can fairly easily get (if outside USA, you'll find them on Amazon USA!).
Other possibilities are, your tv might have a "volume limiter" built in, or, if on "home cinema" sound, set to "mono" and switch off the surround channel (which removes SOME of the unwanted distracting noise, that tends to make speech hard to hear!).
Inside USA there's gadgets like this (& others similar):
The actual problem is audio dynamic range, often very heavily compressed on adverts to mak them sound "punchy"
In the USA, this problem has recently been legislated on (federally):