The answer is a bit complicated, but there are two major parts to it:
1) The tax filing prep companies spend ridiculous amounts lobbying to ensure both that the tax system remains complex, and that they are the only way to deal with that complexity. Fortunately, the effectiveness of this has been gradually waning, leading to things like the new service the article describes.
2) Taxes in the US are genuinely quite complicated, for some good reasons, many bad ones (including the aforementioned lobbying), and even more neutral-but-complicated ones. Both major political parties have a tendency to add extra complexity to the tax code for their own ideological (and often purely political) reasons.
(But despite what many people like to propose in response to this, a flat tax wouldn't actually make things better, because progressive taxation is very important for mitigating the staggering inequality in our current system, and is not even the primary cause of the complexity. The primary cause is the difficulty of agreeing on exactly what constitutes "income", combined with many often-conflicting attempts to incentivize or disincentivize various things through the tax code.)
Taxes are genuinely quite complicated in many countries (Germany's patchwork of feudal church obligations, diffuse taxing authority spread over multiple layers of government, and "temporary" taxes lasting over a century has some fun surprises, e.g.), and almost nobody ever voluntarily reduces the tax code's complexity.
What really sets the US apart is 1, very few other countries manage to witness so much criminal energy getting put into legislation without simply collapsing.
1) The tax filing prep companies spend ridiculous amounts lobbying to ensure both that the tax system remains complex, and that they are the only way to deal with that complexity. Fortunately, the effectiveness of this has been gradually waning, leading to things like the new service the article describes.
2) Taxes in the US are genuinely quite complicated, for some good reasons, many bad ones (including the aforementioned lobbying), and even more neutral-but-complicated ones. Both major political parties have a tendency to add extra complexity to the tax code for their own ideological (and often purely political) reasons.
(But despite what many people like to propose in response to this, a flat tax wouldn't actually make things better, because progressive taxation is very important for mitigating the staggering inequality in our current system, and is not even the primary cause of the complexity. The primary cause is the difficulty of agreeing on exactly what constitutes "income", combined with many often-conflicting attempts to incentivize or disincentivize various things through the tax code.)