Because your future networking potential—and therefore future job prospects—depends on being liked by your peers, who may not choose the same moment of departure as you would. Follow standards and work towards long-term maintainability not because you see yourself at the same company in 2 years but because your coworkers might see themselves there and you want them to like you and feel good about recommending you to their network.
Why?
Why would they want to help you along? They burn capital referring you, they burn even more when you make a mess of things. When you leave a burning husk behind everywhere you go your own network of people who trust you is minimal, so you're not an asset to have around them. Why would they want to help you instead of finding people to con who can actually be an asset to them? In this entirely self-centered world you've put together, what's in it for them?
Referring people for no other reason than that you know them works great, since it will implicitly happen in reverse too. See e.g. the Freemasons.
> They burn capital referring you? They burn capital referring you, they burn even more when you make a mess of things.
They burn capital if hiring you seems like a failure, they win if it seems like a success. That means your incentives are aligned. No-one gets dinged for hiring someone who implemented a couple of buzzwords, left after a couple of years for a higher position elsewhere (or got promoted into management), and then the project they were on failed a few years further down the line for unrelated reasons. Quite the opposite.