Two comments. (1) Lawyers don't write it so simply because if you write ''You pay me for this, I do this for you. Sign here''? there is still the question of when, and exactly what "this is" and what happens if only part of "this" or none of "this" is completed and if there is pay for partial or late. There is also issues of ownership of "this" that should be specified so the product can be resold without entanglements and lastly liability if someone is hurt while doing "this" and how long can be expected before that check arrives.

If you hammer all of that out ahead of time... well you may not need it but if you do it'll save a lot of time, effort and costs after the fact. Now imagine a more complicated pay you this for that and you can see how Lawyers end up with massive documents to deal with.

(2) You should consider the source of your letter is on proletariatpictures website. Since proletariat is a term used by Marx and Engel I suspect there might be some biases there towards everyone working for free, happily together, for the greater good which rarely exists among professionals without gulags and gunshots. Yeah I'm speaking from ignorance here as I haven't read the site but the fact that they named their company that says something.