Generally, most of the tissues in a box are folded in an interlocking manner, such that one sticks out of the box, and when you pull that one out, the top half of the next one is pulled out of the box. But - at least for the brands that I buy (generally Kleenex, but sometimes Kirkland) and I think others as well - the first two are generally folded together, such that you need to pull both out together.
The only thing I can think of is that since the first pull is removing tissue(s) that are completely inside the box, a single tissue is too thin and would rip, so they double it to give it more strength. After that point you’re pulling out tissues that are already half-way out, so even a single tissue can withstand that.
I’m going to take a SWAG.
I’m thinking about 1000’s of tissues being processed at once. My machine that does the folding of the tissues interlaces the first 249 sheets in order but the 250th sheet is folded back into the 249th.
This means that I don’t have 1000s of interlacing sheets. I now have convenient blocks of 250 sheets that won’t rip as I individually move the block of 250 into the tissue box.
I have no true knowledge of this but it seems it may just be part of the packaging logic.
On returning from a vacation, I began fancy fan-folding my gf’s toilet paper each night before going to bed. It took a few days, but eventually she had a ‘waitaminute’ moment when she realized something weird was happening.