Sorry about the title. But I will start with something easy.
I had my first proper summer holiday job in 1962. The end of term coincided with my 15th birthday and I was able to go and work for the London Trustee Savings Bank head office in Fleet Street. I commuted up and down from my home to Charing Cross (hating it and vowing never to do it again). I forget how much I was paid.
I worked in an office where the task was to reconcile all the figures from all the branches. This was easier said than done. Some of the work involved phone calls. To avoid ambiguity, the permanent clerks in the office pronounced the number 30 as thur - tie, 40 as four - tie and so on in order to avoid confusion with 13, 14 and so on - these numbers being pronounced normally.
Now to have the pronunciation of numbers like 13 and 30 so similar as they are in English is dysfunctional. The bank clerks had found a fix for the problem but it has not penetrated to a wider society - fifty years later, we still pronounce thirty in a way which allows confusion with thirteen and vice versa.
So things which are dysfunctional - or if you prefer, less than optimally functional - do not always get eliminated, whether by some Darwinian-like process of selection or by conscious decision.
In respect to this little bit of the language, our practice is less functional than French (treize, trente; quatorze, quarante) or German (dreizehn, dreizig; vierzehn, vierzig) or ... the list continues.
But at another level, English has greater functionality than - say - German. German has three cases (Der, Die, Das: masculine, feminine, neuter) and all these prefixes and suffixes which sometimes you split and sometimes you don't. German is a pain in the arse to learn, which is why if the 27 member states of the European Union had to choose just one language to work in they would choose English. Spanish might be the best second (or even first) choice in terms of second language learnability.
But the moral so far is this: dysfunctional and, more generally, sub-optimal states of institutions and practices can persist indefinitely. They don't necessarily get eliminated any more than do pandas (who are terribly ill-adapted to their environment and generally miserable in consequence).
To continue the story -and to use an example I have used before - consider that the UK has no coherent system of weights and measures in general use and consequently no coherent system it can teach in schools. This has economic costs and will occasionally cause tragedies, as when nurses aren't fluent in the system used to measure medicine doses.
Dysfunctionality can persist at all levels nor is it necessarily the case that people can organise themselves to get into a better ( more optimal) state. As I write, Italians are voting. It seems all but certain that their votes will turn into outcomes which condemn their society to further decline. And they can't stop it even if they can recognise it. Italians are lemmings who know where they are headed.