It is literally a different type of snow....
It is said that the Inuit people of the Canadian arctic have seven different words for the different types of snow. Yup, 'makes sense to me! I have literally spent more money on snow clearing/grass cutting equipment for my home runway, than either of my three planes cost me. Snow clearing cost is an investment you can choose to make or not, based upon your sense of whether you need to fly when it's snowy or not, and your guess as to how often there will be enough snow to need to clear. Three winters ago, I only cleared snow three times all winter, this winter, very different!
Airport operators will serve the needs of the users of the airport, who will have to pay for those services. If you want the runways always clear, it can be done - for a cost! But a part of that cost is capital equipment, which will just sit and cost money if not used, so it's a business case as to whether it's worth the cost, if heavy snow is infrequent.
Here in Canada, we can expect that once it snows, melting away quickly is unlikely, 'cause it'll stay cold, so better clear it. In other places, even a heavy snowfall will likely met away in a day or so, so its a big cost to clear it early, knowing that it will melt away anyway. That kind of snow, as mentioned, will be wet and heavy = extra work to clear. The very cold not likely to melt away soon snow is light and fluffy, and easy to snowblow away - once you buy the snowblower!