Several people have done similar things, and you are correct. It is very possible to simply hack a normal inkjet printer into becoming a 3DP printer. It all depends on what requirements you have. For a single proof of concept project, hacking an inkjet printer is perfect, it is fast, relatively cheap and accurate. However, when you want to make the next step, you quickly run into problems.
When using an inkjet printer, you have little to no control over where and how much ink is deposited. You can slightly influence it, but you have no direct control. For 3DP printing, this can be quite problematic, because the amount of binder deposited in one location is quite important. Also, if you make a project in such a way that others can replicate it, using a complete inkjet printer as a basis is not ideal. The inkjet printer in question might not be available everywhere or might be replaced a year later, and you need skill to hack an inkjet printer.
I tried to make something that did not depend too much on complete, closed source machines. Instead, I tried to create something that is as open as possible, and can be improved upon in a later stage (by both me and others). By doing that, I did have a lot more work and the printer is more expensive, but in the long run, more people will benefit it.
So your thought is correct, but doing it the way you suggested simply didn’t work with my own requirements.
Hope this clears things up.