As an end user of dataloggers I can perhaps give you some user perspective
If it's a small thing I'm trying to stash inside a cover or covertly install outside the last thing I want is 2 antennas to try and deal with. No big deal if they're internal but if they're external it's a headache I don't need.
If it's more "heavy duty" ie designed for long term environmental telemetry, there'll probably only be one omni or yagi on the mast to hook it to. Hydro's aren't RF experts and struggle with the concept of mounting one antenna correctly, give them 2 and they're guaranteed to stuff it up or just not connect one of them.
Final bit of perspective, if it's an all in one unit it needs to be cheap, we have some loggers deployed that are on their 3rd modem technology with the shutdown of 2G services, then 3G services they've now got a 4G serial modem attached. The same loggers could just as easily also have satellite or radio links attached and are infinitely useful
I also have an E waste bin full of all-in-one loggers that have built in 3G modems and will soon be useless. Great loggers that still work perfectly but no good if they can't dial home... If I'm buying something with a built in modem I take its shorter lifespan into account when considering it's price.