In some cases that stupid spinners have only one purpose - to make the one who pay money for the software think that software do something complex and his money worth paying.

Modern computer and networks have enough power and bandwith to make things work faster that human eye could detect. But in dumb moneybags eyes, this make a final product "simple". So, programmers just add that spinners to mock "complexity".

Another case - low programmer skills. Nowdays there are a lot of programming languages with lowest possible entry level. People who are so dumb that they can't understand how computers works, now become programmers. They write extremely inefficient code, because they don't know how things work. Since programming language is purposely made to run any stupid garbage that programmer could write without throwing out error, it finally works, but very inefficiently. This allows to pay much less for programming. Combining that with previously described case, this make managers and CEO's happy.

Really, only rare cases need significant amount of time where that spinners could be reasonable, but usually, competent programmer will use some informative log, describing what computer doing now, instead of that dumb spinner.