Earlier quoted context omitted.
It is mostly because of the social welfare that is funded massively over salaries extortion. Take a random 60k€ salary for a senior software engineer in Paris, the employer is paying at least the same amount of taxes on top of that, making the cost for the company up to 120k€. It is not that far away from some foreign salaries for the same position, except in other countries highly skilled workers are not that massiv…
Honestly. The taxes are only half the story. The other half is that there are simply no company with massive revenues competing for engineers. Nothing to drive price up.
And I'm sure some companies can drive salaries up, they just don't need to. Software engineering is looked down upon, most new grads want to become project manager, somehow working at a big bank / big consulting firm is seen as nobler. Even the recent trend in data science doesn't seem to leverage the education system that is particularly maths/physics heavy.