There are hundreds of ways to end up with a not entirely random arrangement of cards after a shuffle, most commonly as lots of people simply aren't very good at properly shuffling cards. You could reduce this bias by repeated shuffles and washes, but this adds a lot more time and is still not a guarantee. More importantly, though, is how do you convert your series of cards to a usable string of bits without losing entropy or introducing bias? It is not a trivial problem.

The only real implementation of cards to seed phrase I am aware is that on https://iancoleman.io/bip39/. I am not a fan of how it works, though. It assigns different bit values to each card. 32 cards are assigned a 5 bit string, 16 cards are assigned a 4 bit string, and 4 cards are assigned a 2 bit string. 32+16+4 = 52. There are two main issues with this. First of all, it makes some cards 8 times "more secure" than other cards, by way of them contributing 5 bits instead of 2. This simply doesn't make sense. Secondly, it encourages someone to shuffle a deck of cards and then draw them one by one, meaning that once a card has been drawn it can never be drawn again. This reduces entropy, since that particular string of bits will never occur again.

A better way of doing it would be to assign each of the four suits a 2 bit value - spades 00, clubs 01, diamonds 10, hearts 11 - for example. Then draw a single card, write down your two bits, shuffle that card back in to the deck thoroughly, and repeat. This would take much longer than simply flipping a coin though, and still does not eliminate any unknown bias in your shuffles.

I pay zero attention to such metrics. It is easy to fake these numbers with bots, and indeed many malicious wallets do just that to make their app seem more legitimate.