But then why did it take 300 years to explode? Did it just come down to the math? (algebra, calculus, or something else I can't do?) Was it just a tipping point? A few years ago seeing a boar was a novelty, kind of exciting. Then it was like, whoa... what is going on here???
I think a lot of what you are perceiving as a problem is media/internet hype, however, to get to the actual math, maybe historical human example might be helpful. At the time of the Black Plague in 1340s, the human population was estimated at only about 450 million people and the plague likely killed 1/4 to 1/3 of them. In less than 700 years, we surpassed 7 billion people. Keep in mind that pigs breed faster than humans.
http://www.worldometers.info/world-population/
In middle or high school, did you ever do the fruit fly experiment with the jar of agar? I seem to recall that we did a couple of males and four females. and then watched the population grow and then all die. It was seemingly slow at first until it seemed to explode. Population Math.
In the US, our population was only about 3.5 million in 1800 and has gone to over 310 million today. Over 100 million (1/3) of that population growth has occurred since 1970.
http://geography.about.com/od/obtainpopulationdata/a/uspop.htm
Do you know what has gone with that? Pigs. You think the pip population has exploded? It is nothing compared to the human population. However, there is a correlation that is significant. Habitat for hogs, like so many other animals is being compressed by the growing human populations. We see this repeatedly with other game that is also doing well, but being compressed into smaller and smaller areas due to encroachment.
How are we feeding those additional 100 million people from the last 40 years? We can look at crop production. We find that crop production has increased, but not only has it increased, but has become more concentrated in the process as well. For example, in June 1970, winter wheat was listed at 1.076 billion bushels with an average production of 32 bushels per acre. In June 2012, it was up to 1.68 billion bushels with an average production of 47.3 bushels per acre. So that is 50% more wheat per acre than we were getting in 1970. That is some significantly stepped up concentration of resources. Plus, that means winter wheat for June had expanded by about 2 million acres from 1970 to 2012 from 33625000 to 355517970 acres (assuming I got all the math correct).
You can check the ag source if you like, but pretty much most of the crops I checked showed increases in production that were significant over the last 42 years back to 1970. In short, production has increased and yield has increased which means a concentration of resources. Pigs like concentrated resources.
Add to all of this the fact that the pig population is expanding in the US like other animals such as the armadillo (historic, natural invader that first crossed the Rio Grande Valley into Texas around 1850, but didn't start a northerly expansion until about 1900). In about 113 years, the Armadillo has managed to invade 10 additional states without being a game animal or domesticated food animal allowed to free range or turn feral. It isn't bred by the millions on commercial farms here in the US, either. It is limited geographically by its inability to deal with extremes of colder weather, something not as problematic for hogs. While I have not found any population estimates for the armadillo, no doubt the population has multiplied several times over the last 113 years along with its range expansion.
http://armadillo-online.org/expansion.html All in all, that is pretty good for a little critter with a primitive brain, not considered smart like pigs.
In short, you drop a new animal in a habitat where it can grow largely unchecked, and it will do so. Pigs are not a unique example.
So you have a lot going on here. You have concentrated resources, encroachment, growing pig population, range expansion for pigs, growing human population, and then combined with media and internet hype and you have a situation that is significant, but also likely blown out of proportion. If you saw Discovery's "Pig Bomb" or Animal Planet's "Invasion: Mutant Pigs" programs, the notion of being blown out of proportion cannot be overstated. Pig Bomb strongly implied if not outright stated that hogs in the US were growing faster, meaner, and bigger because of the infusion of Russian boar stock and had various scientist and a geneticist on the program to discuss the point, but had ZERO genetic data to prove the point and the geneticist said there were no results. The Mutant Pig program billed the hogs as killing machines that attacked people frequently with seeming regularity.