As I understand it, SP's Chances of Gay/Bi Sim kick in when an undecided teen ages up to YA. Not when new YAs are created. SP immigration might call on this too though, not sure. When a new sim is created or called into being in other ways, their default orientations are either undecided (gender attractions 0/0) or only just barely straight (-1/2) where the first number is pref for same gender and the second number is opposite gender, all as per the game's defaults. Sims' gender prefs are fluid, not static, so what happens from there depends on their social, flirty, and romantic interactions as well as availability -- the lack or overabundance of sims of the preferred gender will play a role when they are just starting out with such delicately low numbers there.

So these 6 straight males, according to MC what exactly are their two pref numbers? NRaas > MC > (Sim) > Intermediate > Gender Prefs. (MC Cheats add-on module required to see this)

In other words, setting those chances to 80 and 20 will not give you 100% gay/bi sims and actually won't have an impact at all right away, until a generation or two ages up. Also, if your goal is to not have straight sims at all as teens age up, those wouldn't be the right settings.

Chance of Gay Sim - this one rolls first.
Chance of Bi Sim - this one rolls only if the first one fails. So what you have dictates that there will be a 20% chance that an aging up teen will be bi if they are not already set as gay. In other words, 20% of the remaining 20%, which would be 4%. What you probably want is something closer to 100 here.

With numbers that delicate, a sim with enough charm and charisma can change their prefs by merely winking at them (or asking their sign if they chat them up first, anyway).

Teens have gender prefs. Could be mistaken, but I don't believe that they budge from 0/0 unless they are flirting, romancing, going to proms, etc. Not all teens are "active" with respect to those activities.