Why does the incorrect plural "aircrafts" seem to be occurring more often?

My first reaction to aircrafts was to think it was a typo, but I just checked usage on NGrams...

...and compared it to usage for the singular / collective noun form aircraft...

...which seems to indicate that the "regular" plural form is gradually being taken up. Does this represent a tendency for English speakers to enforce regularity on the language? Are there any other examples? I'm not expecting to find that "sheeps", for example, is displacing "sheep" for the plural meaning, but maybe there are other "less established" usages that could be changing.

EDIT Please note that I'm not asking whether "aircrafts" is correct, or common. I'm asking if there's any reason why it seems to be occurring more often over recent decades (even though it's still pretty rare). And whether this effect occurs with other nouns having "non-standard" plural forms.

Well, this is an example of why Google NGrams isn't a precise indicator. When we compare the two directly, aircrafts simply can't get off the ground:

Now, this result is also flawed since it is impossible to separate uses of aircraft (singular) and aircraft (plural). It is also impossible to factor out typos (aircrafts vs. aircraft's) and so on.

The point is, don't read too much into what an NGram shows (or at least take the graphs with a grain of salt), because a great deal of the time what you wind up with is this sort of thing:

(BTW, the huge spike in the use of aircraft in the early '40s is almost certainly due to the air war in Europe and the Pacific.)

Graphing some aircraft against some aircrafts shows that the latter is still quite uncommon compared to the former:

I would say that such as it is, it represents a tendency for non-native English speakers to emulate regularity when they do not know that the plural is irregular.

I don't think there's any way to answer this question definitively. All we're doing is speculating. So I'll offer a few speculative theories:

As use of a word rises, so does misuse of a word.

Aircraft saw an increase in usage between 1970 and 1990... and so did aircrafts. Aircraft then trended downward after 1990 and so did aircrafts. Softwares is also on an up-trend, mirroring the trend of software. Interestingly: Sheep saw an uptick in usage around 1910, and so did sheeps. Who knew?

Edit to clarify: In other words: If we speculate that X% of people mis-use aircrafts, as aircraft becomes more widely used, so will aircrafts. @FumbleFingers has pointed out that the use of aircrafts has increased more than use of aircraft. That may be so, but I don't think it invalidates this theory as a contributor to the overall uptick in use of aircrafts.

More writing = More mistakes

The sheer body of work increased dramatically in recent years - 3 billion ngrams in 1970 versus 13 billion in 2000. With writing becoming more accessible to a wider audience, it stands to reason there would be more potential for incorrect word use.

Edit to clarify: Again, simply: If aircraft appears a million times more often, that's a million more chances for typos, mistaken word choice, or things slipping through a proofreader.

English Takes a Beating

Sites like this non-withstanding, I think there's been a pretty clear trend (in the US anyway) away from proper grammar and spelling. As education takes a nosedive, one would expect word misuse to increase. Some folks in other answers have blamed non-native speakers, and maybe that's a part of it, but I think the native speakers are as bad as anyone in this regard :)