I guess the rationale is that you give precedence to the people paying for the healthcare (middleclass workers) to get them back to contributing to workforce (and earning those tax euros) as soon as possible. Also the decision is done by the companies (trying to keep their employees in working condition, also a big perk when employees are comparing different employers) and not the government so you can't just decide to move the money like you just described.
I guess the rationale is that you give precedence to the people paying for the healthcare (middleclass workers) to get them back to contributing to workforce (and earning those tax euros) as soon as possible. Also the decision is done by the companies (trying to keep their employees in working condition, also a big perk when employees are comparing different employers) and not the government so you can't just decide to move the money like you just described.