There’s a belief that Mars once had an atmosphere and that it was stripped away or wandered off. IMHO it has always been just about the way we see it now, and that the drive to send human missions to Mars is the main reason why some insist Mars used to be more or less Earthlike, or that it used to have seas of liquid water (which would require an atmosphere of some sort).
The microbial activity in the Martian soil does suggest that there used to be more atmosphere, but given that the Earth has microbial life as far down into the crust as anyone has ever looked, could mean that’s where all the action happens. Y’know, from a materialist-reductionist perspective.
The solar wind might indeed strip off the atmosphere, if Mars had much of one, but if we were to introduce an Earthlike mixture (78% nitrogen, 21+% oxygen) from frozen gas chunks in the outer Solar System, granted it would be a big job, and take a while, it would be a really long time before Mars would need a refill as it were. ;’)
Thanks for smartsplaining.