SG supplies cards with their cams to ensure you have a good card, and they bundle several different card sizes for you to choose from. Viofo has his card manufacturer test the cards in his cams to ensure functionality (those are MLC type cards and offer long life along with high write speeds). Thinkware and Blackvue want you to use only their own cards which are overpriced, and it can be tough to find any other cards which work in their cams (and it seems they design their cams to be like this).
Since most cam issues are card-related this approach reduces after-sales customer support and warranty claims. Most average drivers are well-served by smaller cards although those wanting to use parking modes need larger ones. Relatively few cards work well in dashcams, so this leaves the manufacturers (and us) sort of corralled into buying only those cards at whatever prices are being charged for them. Then they have to maintain their sales pages accordingly, so if card prices go up they have to change their advertised prices or lose some of the expected profit margin from sales. Card prices are stable right now (and relatively cheap) but it wasn't so long ago that a reliable card cost about twice of what you pay today for the same card. Cards are only expected to last a certain number of write cycles so a card twice as large should last twice as long in addition to offering longer recording times, making them doubly attractive to advanced cam users as long as the prices are good.
At the other end of the spectrum are some cheap cams which come with cards, usually equally cheap and always small in size. That is done more for a marketing edge as the buyer sees the card as a bonus, saving them money over a similar cam with no card. That type of cam buyer will probably never check the card after a very short time of use and they are probably unaware that cards don't last forever too. It's only when they need footage and discover their cam hasn't recorded in months that they end up coming here to DCT to learn which card and cam they should have bought in the first place, and we try to help them find it. The manufacturers and sellers of these cheap cams don't care about their customers after making the initial sale, and often they will not warranty the card, just the cam, then blame whatever the problem was on the card. And though we here preach "only good cards we recommend" the truth is that with cheap low-bitrate cams, most cards will work for awhile at least, even if they don't work in the good higher-bitrate cams we recommend.
You sometimes find a manufacturer or seller recommending certain cards on their sales pages, but cards do change over time as the card manufacturers change the build process or as the raw materials they buy to make cards with change. So this often leaves someone buying a 'recommended' card which actually doesn't work properly. In years past Sandisk cards were well-known for not working well in dashcams, but Lexar cards did. Now some Sandisk cards are great for us but no Lexar cards being made today are. These mentioned cards are likely great for other uses but when you need the high write-speeds our better cams require the whole scene changes on our end. SG recently bundled a card which was thoroughly tested as working well initially, so they bought a lot of the cards only to discover that now there were problems with that card once it reached general distribution. They notified every registered owner of their cams which were sold in that era about the problem to get those cards replaced under warranty. I think they were able to return most of the cards they bought to their supplier seller but I'm sure they took a loss with some of them and it took a lot of time and effort to rectify things. I'm not sure any other cam manufacturer or seller would have went that far, and I'm positive that many wouldn't have done anything. So sometimes even the best effort and intentions aren't enough with SD cards for dashcams and it takes awhile to work things out.
I the 5 years or so I've been in the dashcam 'game' I've watched as all this happened here on DCT, where IMHO you will find both the best people as well as the best and latest info on all things related to dashcams. You won't find a better place for this kind of information in the English language than here. Hang out on DCT and you'll gain from the freely shared up-to-date dashcam expertise found here, and when it comes to dashcams the uninformed masses will look at you with awe and respect regards what you know about dashcams plus it can benefit you too.
Phil