Interesting question, guess i am not the only one. I have had a fish only tank for about ten years, a 50 gallon and have had good success with keeping it healthy. I have a relaxed but constant maintenance program of cleaning, water changes, monitoring, and it works. On the other hand I really want a planted tank and have made four attempts to plant my tank and so far I am at zero for plants. My first attempt many years ago involved buying plants and sticking them in my pebbles. Each of the subsequent three attempts were preceded with some research and modifications to the tank designed to allow plant growth. My forth attempt ended about three months ago and had pressure CO2 and PPO fert program added to what I had. My forth attempt was decidedly my worst attempt as I spent a lot of money and not only did my plants die I had the worst algae problem ever.
I think a smart person would quit trying after achieving the results I have. Guess I am stuborn and have spent the last month reading everything I could find on growing aquarium plants from basic to advanced topics. Everyone has their own ideas but it is confusing many times for someone after answers when many times you get answers that not only conflict but are opposites. I am preparing to begin my fifth attempt and have been busy asking questions. Those questions have targeted the three basic requirements for plants, light, food, and CO2. And I have received answers which conflict. So, part of the answer to the root question has to be the confusion a new comer faces when beginning.
For my fifth attempt I have just finished changing my pebble substrate for a plant friendly substrate. [In point of fact I have read at multiple places that substrate is not really important and I have read that it is all important.] I have a 2 bulb T5HO fixture in a 48" tank and have upgraded to 6700K bulbs. I have read that with this set up I have too much light and I have read that I have just a bear minimum amount. I don't have a par meter and don't want to invest in one at this point. So, I believe I will begin my fifth attempt with just one of my bulbs on and see what that does. I have read that plants won't grow without food but I have also read that you should not fertilize at the begining, maybe for the first month or two. I plan to not fertilize to start and see what happens. And, I have read that for hardy low light plants I do not need CO2 and I have read that I won't get good plant growth without CO2. I plant to start without my CO2 system turned on as I will again start with low light easy plants.
So, confusion and resultant poor results certainly have caused me to start and stop several times along with the continual cost of experimenting with changes.