Don't throw away washed towels. Whiten them according to the old recipe

Every time I visit hotels or on vacation, I am amazed at the impeccable cleanliness of the linen. Bedding and towels, dare I say it, shine white. It seems like they have a special secret that no one knows about.
Once at a small hotel in St. Petersburg, at the reception staff we gave a box of large pink home-grown tomatoes to the staff in exchange for showing them the powder used to wash clothes. They showed us an ordinary gel in a ten-liter canister, which is freely sold at Wildberries.
Why does white linen and towels at home acquire a gray tint over time, because I use modern, good quality products and dirty linen is not dirty at all?
Often on the Internet you come across videos of how towels are bleached using laundry soap and potassium permanganate. Indeed, before our eyes the fabric turns white. I always trust recipes that contain laundry soap, because it really removes stains on white and colored clothes.
I decided to try it.
I attached a new white towel for comparison.
1) Folded the towels and put them in the basin. I poured hot water over them so that they were saturated but not floating.
2) Next I took 72% laundry soap.
3) Rub the towels well on both sides. When pressed, foam comes out.
4) I left it like this overnight. I rinsed it in the morning.
5) I poured hot water into the basin and added a little potassium permanganate, just a little, on the tip of a knife. The water turned dark crimson.
6) Each towel was dipped in this solution in turn. The terry immediately turns brown, but when wrung out, the fabric returns to white. You need to keep just a little bit of manganese, just swirl it around a little in water.
7) I can’t say that the towels became snow-white after this.
Next I finished washing it in the washing machine. The experiment was 70% successful.
As a result, the towels became whiter, but not enough to compare with a new towel.
And in the video I watched, the towels became snow-white.
All the best!