The 'scrapping the MOT' concept referred by GB and its effect of slackening people's attitudes to their machines may well be right in some cases, I don't disagree with that at all. And Rex's point is spot on. But as Mitch says, not in all cases.
However, in countries where there has never been an MOT equivalent, like France, it's a moot point. And will remain one, now that the latest EU-driven attempt to impose regular tests has been scrapped through the unceasing efforts of the various motorcycle associations over here. The FFMC - Federation of French Motorcyclists 'en colère' (angry) is a formidable Motorcyclists' Action Group-like organisation.
Despite that, I wouldn't say the prevalence of clearly unroadworthy unrestored machines is any higher here than in the UK because most are well looked-after with their patina protected carefully - but the existence of some unroadworthy machines, restored or not, can't be gainsaid.
If there is one give-away for me it's the widespread use of solderless screw-on nipples on BRAKE cables . . . (for chrissake). I'm not sure if some makers actually used these things from new on lightweights or whatever . . . but when I see them used on quite potent machines it gives me that churning feeling in the guts.
A second clue is the failure to have any semblance of a working electrical system, apart from a magneto. In France, pre-'65 stuff doesn't need lights on by day (unlike in say Germany or Spain) but the lights are supposed to work if required. A lot of machines don't even have a battery fitted, let alone a working generator.
The advent of the Alton alternator, made here of course, has led to a significant improvement among Brit iron owners prepared to invest, but that still leaves a lot of blacked-out beasts trundling around. It's to be hoped that the proportion with illuminations will continue steadily to improve. (In this department, lightweights are often 'better' owing to their simple flywheel alternators.)
Frequency of 'failure to proceed' is a reasonable indicator of how well things are maintained I guess.
In the 20+ years I've been playing in France, the incidence of breakdowns on days out, and the signs of neglect and / or glaring incompetence have reduced considerably luckily, to the extent that quite often a support van or trailer isn't needed even for quite adventurous excursions. So there has been an overall improvement in habits, as breakdowns were part and parcel of most outings 15 or more years ago.
But when it comes to the few that do pack up, it's a quid to a pinch of s**t it's a shiny one!