"Simple import script"
That's simple to type the words of, agreed. Actually writing such a thing, well, I suspect the only person who would think it simple is someone who has never tried something like that, particularly for totally non documented proprietary forum and cms software, integrated into a single package. But it is very easy to type that something is simple, so I guess that part is correct.
Possible, yes, simple, almost certainly not. Translating the urls alone would be probably almost but not quite impossible, resulting in a full loss of all links to those threads all around the internet, as well internally in the bpl site itself, always a fun result of moving sites without proper handling of the urls. Again, possible, yes, simple, no.
The urls is another part of the thing, if they were done reasonably well to begin with, you could translate them fairly easily, but these weren't done using text strings so it's pretty hard.
Having actually moved sites with no loss of links or structure in the process, or at least, redirected (correctly) changes, beyond some irrelevant stuff, I can assure you that it's not simple. Trying to translate one forum+cms type db structure to a totally different one, oh, the fun. That kind of thing requires either paying someone a lot of money, or having the great fortune to happen to have available someone who will do it for either a massively reduced, non market rate, or for free. The odds of someone with that technical expertise feeling like doing that for free and being a bpl member, not so high, but not out of the question I guess.
This is of course a case study in why NOT to ever use these types of tempting web hoster run proprietary 'solutions' to putting up a website, long term, it will always need to be redone, and it won't be easy, and usually, the web devs don't even try to actually import the old parts, they just dump the content and move on, because, sadly, in fact, it's not simple to do that.