Why is 16 Bit file so large?

[SuCCeSSvS]

Adobe Photoshop Version: 23.1.1 20220106.r.202 060a6d1 x64.
I have a File, In 8 Bit the PSD weights 3MB, in 16 Bit its 181Mb, I understand 16 Bit switches from 256 tonal values to 65,536 tonal values, but this doesn't seem right, In what state of mind would anyone besides some famous artist with 10Tb of space choose 16bit over 8 bit, I have around 60PSDs with a similar amount of work done, it all adds us to 2Gb total, if I were to x60 the file size (from 3MB to 181 MB each file) that's 120 gigs. anyway, I am just curious is this how it's supposed to be?
I also did an experiment, I created a PSD thats 4500pixels by 4500, (I use that by default for my project) and I just drew a line, and saved it, in 8bit it was 2MB, in 16 bit it became 154MB!!!!!! Please help 

[TheDigitalDog]

All high bit documents are (without layers) twice the size of their 8-bit per color cousins. Layers increase this as well and what's on the layer plays a role. So a 'virgin' 3MB document in 8-bits pre color should be 6MB in high bit (what Photoshop calls 16-bit but really isn't). So there must be something else going on here. IF you are converting 8-bit per color data to 16-bit and Dither is on in color settings, that could be the cause of the larger size. But it is pointless to convert 8-bit per color data to 16-bit.