It's not so much about them being profitable but more about them being available to play for everyone who wants to play with them. How can we get new players to stick with us when they see they can't get some of the important cards because they are super expensive even though most old players have them? Or worse, if the cost is high and there's a time limit to unlock and when they join they simply can't find the card. They're gonna give up when they see they can't access the card. Anyway, if I'm going to sell them, I still want to profit and not have to gamble taking a huge loss.
Those GFL that cost 100x are from older sets with very low print run. These cards have a high print run but you want to artificially make them expensive.
At that point I'd rather have them stay soulbound forever and use a similar system to dust in hearthstone where you can burn cards for dust and use it to get other cards. We could apply that to soulbound cards and allow it to be used on older and newer soulbound cards.