I hear what you're saying, and honestly for the most part I agree. It would be SO METAL to see an isekai series actual take how things would actually be in a historic setting into account, buuuuut on the flipside I also totally understand why most isekai don't go into this route. It's supposed to be shameless wish fulfillment and having characters struggle with there not being modern appliances or having horsepoop litter the street as mothers bury their 16th dead baby wouldn't be exactly the cheery bright fun that most people are looking for with their fantasy these days.
Though on that note I have kind of wondered what would it be like if an isekai protagonist brought a modern day disease into an isekai world. Like say, just randomly off the top of my head, covid-19. There are obviously way more obvious choices than that but that disease is what's hot in the streets right now and I think it'd be interesting to see how a fantasy world would deal with the pandemic we are facing with right now.