The two factors responsible for this difference in prices are VAT (value-added tax) and commuter traffic.
Prices for personal plans are including 21% VAT. The VAT is paid to the tax authorities in whole. The prices voor business are exluding VAT, because businesses can reclaim the VAT they pay at the relevant tax authority. Therefore, VAT is irrelevant for businesses.
So, when we compare the personal and business prices including VAT, the prices for businesses are in fact higher than the prices for personal plans. These prices differ because of commuter traffic. We feel that carbon emissions as a result of commuter traffic should be compensated by the employer, not the employee. That's why, for businesses, commuter traffic is included in the average carbon footprint calculations, and prices are a bit higher.