The "transport investment of the decade" at Érd alsó

I myself wouldn’t call the building of a correct platform and an intermodal bus station nearby be a very remarkable investment, more one that is a minimum from the city. Of course, this should mean building of shops, restaurants and proper service at the combined station as well.
Now will somebody tell me, that why herds of buses are used to transport people from this station to the city centre, instead of trains?