This looks like a very typical audio recording UI element. The bars are animated to the volume of the recorded audio. Helps the user see that the application is picking up their mic.
It's a digital analog of a VU meter on a mixing console, though the UI has morphed over time. (Like that the lines vertically centered, vs. being on aligned bottom like you might see on a real-world meter.)
… because it doesn't need to be bigger…? The purpose is to convey that "hey, the audio equipment is working". I use these all day to debug things like "am I not recording, or is the other side's volume muted?" We need "videoconferencing" or "notetaking" app levels of accuracy; it's not a sound studio app?
Not to mention how much dB as a unit freaks people out.
It's a digital analog of a VU meter on a mixing console, though the UI has morphed over time. (Like that the lines vertically centered, vs. being on aligned bottom like you might see on a real-world meter.)