The average workplace has so much background noise - people on calls, the photocopier, others talking - that a very quietly spoken mumbling colleague, especially if they always turn their head away or cover their mouth, or worse, if there's a sodding radio playing as well, is impossible to hear for many people, whether they have had hearing issues all their life, whether they are experiencing age related deterioration or whether it's auditory processing issues or whether it's Tinnitus. Or it's just too loud in there and you're too far away for anybody to be able to work out what you're saying.
You're potentially taking offence at somebody's disability and making it all about you, when what you actually need to be doing is listening to what they are telling you (ironically enough).
They can't hear you.
Do you need to reduce background noise?
Do you need to speak more clearly?
Do you need to face them so that they can get more of what you are saying through the movement of your lips? (Not necessarily lipreading, it's more like scaffolding for the sounds that can be heard sometimes, as lipreading is a separate skill).
Do you need to just walk five steps so they have a fighting chance of hearing what you are saying, rather than guess what it was from across the office whilst somebody's got the radio on, five people are on the phone, somebody's doing a massive print run of booklets and there's another person bringing in a delivery and clattering around in the doorway?