Because more and more people have recognized that it’s much healthier in the long run to not have feet get too out of balanced. It’ SO much better for the entire body for feet to stay more balanced, more regularly, then go from perfect to too-long, to perfect, to too-long, back and forth for years.
Even if the foot grows such that it only gets taller, and doesn’t break the HPA, those heels are still running forward, which is starting to pinch the back of the foot. Repeat those couple of weeks, cycle after cycle, year after hear, and you’re inviting hoof issues you didn’t need to invite. And it’s not even about a farrier leaving the foot long to begin with, it’s about the amount of growth in that amount of time.
Now, if the feet aren’t growing fast enough to get that much out of balance by 7-8 week then by all means don’t trim more often, That’s not the norm though, especially for shod feet whose growth isn’t being mitigated by any wear.
Thankfully, some “trends” are because we know better so can do better.