Oakwood isn’t just in Wales; it’s probably in one of the least accessible parts of Wales from the rest of the UK. If it were somewhere in South East Wales near to Cardiff or Swansea, or in North East Wales near to Wrexham (as just some examples), then you’re very near to a big proportion of Wales’ population and also accessible to a fair proportion of England for a day trip. Cardiff is only ~2h from Birmingham, ~1h 30m from Worcester and ~1h from Gloucester, Cheltenham and Bristol. Wrexham is ~30m from Chester, ~30m from Liverpool, ~1h from Manchester and Stoke-on-Trent and ~1h 30m from Birmingham.
Oakwood, on the other hand… yes, Pembrokeshire is a fairly popular holiday destination, but the only vaguely major population centre that is less than a 2 hour drive from it is Swansea, and unless you’re like me and live extremely close to the South Wales border, then Oakwood is likely to be a 3hr+ drive for you if you live in England (and likely an utterly ludicrous drive if you live in Scotland…). For some perspective, I’m based in the Forest of Dean, less than 10 miles from the South Wales border in Chepstow, and Oakwood is 2.5 hours from me… even for me who’s very close to the Welsh border, it’s the very furthest I’d feasibly be able to travel for a day trip. I went there on a school trip once; my secondary school was literally on the Welsh border, and it took nearly 3 hours to get there by coach.
If it had been located even a little bit further east, I feel like its success prospects would be somewhat greater. There clearly is a market for the park, or else it wouldn’t be here today, but I feel like that market would have been greater had it been located elsewhere in Wales.