Who can't speak for FoolHQ or the company's finances but from what he understands, it was a technology reasons that led to the UK boards being shut down, not the financial cost... and The UK boards are closing because the site is moving to a new platform.
I only mention those extracts as we are often told here (on TLF) that the closure was a matter of costs.
I recall telling my mate about TMF, and he signed up. A week later down the pub he remarked "that bloody site you recommended, my inbox is flooded with spam since I signed up". And then TMF closed its UK boards down. So I think "technical issues" was exactly the reason, either that or a lack of will to keep them secured.
That sounds more likely to be a user-education/friendliness issue than a technical issue - sites often have their default settings for new users set to say that they want the site's routine emails, at least unless they take care during the signing-up process to tick unticked-by-default or untick ticked-by-default boxes (as the case may be for the particular site) to say that they don't want them. If one fails to do that, it can usually be fixed by exploring one's profile on the site until one finds where one can turn the emails off, but sites vary about how easy they make it to find it...
I can't say anything from personal experience about how good or bad TMF was in that respect, beyond a very vague recollection that I did make some profile changes in the area at one point, that isn't necessarily about TMF - it might be 'crosstalk' from my experience of some other site. The fact that I find myself unable to say anything more about it i's almost certainly due to the fact that I signed up to TMF a few months short of 20 years ago!
My other comment is that there isn't necessarily a conflict between TMF deciding to shut down the boards for technical reasons and for costs reasons. Technical issues to do with their board software being old and clunky might well have been causing the moderators and other staff to take more time doing the job of maintaining the boards, which raises the proportion of their wages that is being spent on paying them to maintain the boards and thus raises the costs of the boards; technical issues to do with the supplier of an outsourced part of the boards software system no longer supporting them might well have been raising the costs of keeping them running and/or making it necessary to invest in a replacement for that part; and those are just the first two ways I happened to think of that technical issues could cause costs issues...