They can be grouped in following two broad categories:
1) Those who are always looking for the next best thing, due to some underlying issue that prevents them from forming a long term relationship. OR,
2) The ones who have a Peter Pan complex and just never want to grow up.
Most of these toxic bachelors seriously consider settling down once they have a mid-life crisis and see the writing on the wall. Then they try to get married in a hurry to have kids, and to ensure their own immortality through their offspring.
*40 is a race-dependent number. Asians can be considered toxic bachelors if they remain single past 31.