There is cartilage, fats, cell structure, and a ton of other things that make up the majority of meat that are extremely difficult to replicate for texture both when it is first cooked/heated/whatever and how it holds up as leftovers. Like different cuts of meat are basically the same parts but wildly different in taste and texture just like plants are basically the same except for all their differences.
Honestly I don’t get why so many people want a fake version of meat made out of plants when plants are pretty awesome on their own. grilled vegetables are fantastic! There are a ton of cultures with meals that are vegetarian or vegan and very complex in both flavor and texture because they played to the strengths of their available foods. Why bother with trying to make mediocre fake sausage when spring rolls exist?