There's a good chance that you never exactly believed writing to be especially simplistic. In fact, maybe you know from first hand experience that writing anything from a lab report to a poem requires hard work. Translating the ideas from your head to the paper is nothing short of frustrating and downright difficult. In fact, often times, you have to rethink your thoughts, rearrange words, or revise the syntaxs of your sentences just to effectively communicate a specific idea.
A lot of individuals seem to think that writing comes easily to certain people and that they're born with this innate talent. However, that couldn't be further from the truth. Most people don't realize that for every one line I've written in one poem, there were like five other stanzas that just didn't make the cut. That's the difficult part about writing. You never know what could be in your end product, yet so many people think that talented writers have their first thoughts make it into their final product. Overall, like a skill, writing is something that requires time and effort to finesse. If you don't put in the time, you can't expect to be an expert. In fact, my creative writing professor once told me that the writers working today weren't necessarily the best at their craft, but they were the most persistent.
Also, writer's block is a very real thing that happens to most people. Creating something from nothing is a difficult task. Staring at a blank page and wondering how you're going to go about constructing something original seems daunting. Perhaps, it is the reason so many writers are prone to procrastination, which is even worse considering real writers have due dates and deadlines.
I guess the struggle is worth it. If you ever experience the joy of being published and having something tactile to hold and point to that showcases a work of your writing, then you know that nothing could possibly beat that feeling. That's why you continue to put up with the frustrations, and you keep going.