You need to supplement vegetables with many substances that are not required when eating enough animal food.
However, when buying food that is labelled as vegan this is not always obvious, because it might already include various supplements, and also some of the supplements required by vegetable food can be obtained from minerals, so it is easy to get them while avoiding animal sources.
The most important substances that are not contained in adequate quantities in vegetables: vitamin B12, vitamin D, DHA (omega-3 fatty acid), EPA (omega-3 fatty acid), choline, taurine, iodine, calcium, sodium.
While everybody mentions that it is possible to get an adequate intake of proteins by mixing cereals with legumes, what is not usually discussed is that the quantities that must be eaten are quite large.
For example an adequate daily protein intake for a male of my weight is provided by 500 g of wheat floor plus 167 g of lentils per day.
Someone who does heavy physical work might be able to eat so much in a day, but if I would eat this quantity, I would gain weight extremely fast, because wheat floor and lentils contain much more starch than proteins, so they provide too much energy.
So the only way to eat that quantity, is to divide the wheat floor into 2 half portions, use one for home-made bread and the other for making gluten, while dumping the starch from it.
Only by wasting time with making gluten at home, it is possible to eat enough vegan proteins while also spending less money than when eating meat.
In Europe, where I live, the cost of proteins from chicken breast is 3 times the cost of proteins from wheat floor and 2.5 times the cost of proteins from lentils.
So if you buy wheat floor and lentils and you cook them at home, it would be cheaper than buying chicken breast.
If you buy any kind of processed food made from vegetables, you end spending much more for ensuring an adequate protein intake than when buying chicken breast.
Even bread costs 2 to 6 times more per protein content than wheat floor, so only the most basic bread is cheaper than chicken breast. The commercial protein extracts from vegetables, aimed at vegans, have a price many times higher than meat.
In conclusion, I also agree that "a balanced meat-free diet is not easy".
There are only 2 choices to achieve it, either spend much more money than a meat-eater, or spend more time with cooking at home than a meat-eater.
There are also many vegans who do not know how to supplement correctly their food, because they repeat the myth that "only B12 is needed", so they eventually develop various health problems, as also testified in a few of the other comments posted here.