I asked the question because I’ve noticed it a lot recently (the last few years). Trouble is, as marinelife mentions, ‘loosing’ means something quite different.
So, “I’m sick of loosing my underpants at the laundromat” sounds like the complaint of a compulsive streaker, not someone who can’t find their missing underpants.
I blame the internet because people see the careless spelling of others much more than they otherwise would. So much so that they eventually start to get bolshie about it and claim that there’s nothing wrong with spelling it that way, “Get with it grandpops! It’s how I roll!”.
This is why we have L8tr (later) and teh (the) and wuz and coz and rite and etc etc etc.
My fear is some day the hoards will rise up in cohesion and declare the new spelling of ‘Lose’ to be ‘Loose’ and ‘Loosing’ to be a fine replacement for ‘Losing’.