The reasons may be
1. Vodafone staff work in a "no seat" environment meaning they have to stand all day long which would be difficult for a person who is fasting
2. They have to continue their normal working hours even during Ramadan. As per law, you cannot force a muslim worker to do long working hours.
3. Customer interaction needs lot of communication which would dry you out if you are fasting.
4. Most of the muslim staff may have obtain their vacation leave during this period
5. They want people who can continue to work even during eid

These are my personal ideas and do not represent any institution or person in any way