Why not? 2G might be old, but that doens't mean it's bad. 2G has a few advantages over 3G and 4G: equipment price and coverage. The costs for 2G equipment are lower due to licensing, patents and all that being expired (although that's just small change when compared to the price of a train set) but the main benefit of 2G is that it's got tremendous coverage!
A few years ago I was on a MyFerryLink ferry from Calais to Dover. I had 2G coverage all the way through, there was only a brief interruption when my phone hopped from the SFR network to the EE one.
Furthermore, the amount of information that has to be provided to the trains should be small: "You are train XYZ123, you are a fast Thameslink service, and today you will be stopping at stations A, B, C and your service will terminate at D." You don't need 3G or 4G technologies to relay that.
2G is bad because in so many places it's near useless for data. Especially on O2 and Vodafone, or using old Orange sites get to be brought into MBNL. Usually with copper backhaul or microwave links with woefully inadequate capacity to cope. Besides sometimes having no data flow, you can often have speeds so slow that things timeout.
Ironically, once a site is upgraded and gets fast 3G and/or 4G, then GPRS and EDGE can become quite good but until all sites are done, I wouldn't recommend using 2G at all.
3G is also flawed due to cell breathing, so you really want 4G, which even with a poor signal can maintain a usable, low latency, connection that is fine for small bursts of data. Suffice to say many M2M systems, like smart meters, are going to 4/4.5G. Especially important when 3G will be turned off in many places by 2020.
2G is fine for the railway with a private network, but otherwise a no no.
Does anyone know what network is used?