Actually it is the camera. The oldest cards were recorded with a 720p camera. More recent cards were recorded with a 1080p camera. The newest cards are recorded with a 4K camera. Over the years the post-production software used has also improved in quality.

There are some cards that were recorded in 4K, but only released as standard quality in 720p and 1080p. Totem is gradually reprocessing those cards using the current software and releasing them as crystal clear cards in 720p, 1080p and 3K. A crystal clear card in 720p looks a bit better than an older medium quality 720p card because of the better post processing.

Some of the cards currently available only in 720p were recorded with a 1080p camera. They could be reprocesses and released as standard quality in both 720p and 1080p. Totem has done a few, but their priority seems to be upgrading standard to crystal clear.

I find that I can play both 3K and 1080p cards on my 4K display with acceptable results. (I can tell the difference, but I'm willing to tolerate 1080p for a card I like. I only play 720p cards in small mode with a reduced size setting because the are too blurry for me when played at size setting I normally use. That's unfortunate because some great models are only available in 720p.