Thank you all for the pointers!
Found the issue! Well, it's sort of compound of the two components. Engine ground cable and starter switch.
After taking off starter and plugging it directly to the battery, starter was working as if nothing happened. Opened it up anyways just to check if brushes are on the last leg or bearing is dry. Nothing of sorts, seems that it has even been replaced recently.
Put it all back together. Tried starting the bike and it's the same - no humming or any signs of the starter even trying to turn the engine over, decomp solenoid and starter relay were making click sound like before.
Checked engine ground cable connector from the battery to the casing bolt and it was slightly rusty so after cleaning it up, starter started engaging every other push of a button. For those who are looking for the location, I am attaching pictures.
I've also noticed that the starter would only turn over depending on how I pressed the button so I thought I would open up the switch. Sure enough, it was pretty filthy so cleaned it all up.
Now it cranks every.single.time