You are indeed correct with observing that the male lead in Shonen or Sentai showsis usually getting the brash-and-angry "boy" template.

As for the why: well, this is connected to the Japanese

concept of masculinity (more specifically, adolescent masculinity). A stereotypical "boy" in Japanese contemporary shonen fiction is supposed to be headstrong, have a rough language, a rash base attitude, an extremely high damage tolerance, a couple of bruises and band-aids... and is likely to constantly get into fights with others.

That's considered "manly" or "boyly" in this context, which is what the audience of those shows (Japanese boys) is looking for. Ramped up to the max, you end up with a "rebelling delinquent" lead - another extremely popular character archetype in the genre.

Rin Okumura, one of the more typical "Angry Boys".

That being said, your selection is quite biased - as the situation changes drastically as soon as we go beyond the typical shounen hero age bracket up to age 20. Any male lead character beyond that age usually gets a very different template: the "cool badass" (for lack of a better term).

This archetype is no longer the "perfect boy", but instead the "perfect man" - and these cool badasses are just as common. In fact, they constitute the entire rest of the action-themed protagonists in Japanese fiction.

Kiritsugu Emiya, showcasing what these boys become: the "Cool Badass".

These "cool badasses" are characterized by their always-calm appearance as well their rigid emotional and situational control. He is absolutely no stranger to violence, but contrary to the brash and charging shounen, he puts a lot of value on intellect, calmness and style. Arguably, we can find a lot of ideals from the Bushido / Samurai code resurrected here. (courage paired with emotional restraint, intellect, sophistication, honor...) Should you ever see one of these rage and scream, then it means something went very wrong for him just now.

One title where you can directly observe both sides of the equation would be Fate/Stay Night , especially with its constellation Emiya Shirou <--> Archer.

<Warning: Fate universe spoiler to follow>
Fate has both archetypes in various places, but one character even illustrates how one turns into the other over time. First, we have Emiya Shirou, the adolescent male lead of FSN, and he definitely shows his share of shounen behaviour. He is headstrong, courageous, and more often than not, rash in his actions. Second, we have Archer, an accomplished warrior who has seen many battles. Calm and composed to the point of being deadpan, stylish, reticent, honorable and sometimes cynical. A pretty precise example of a cool badass. The catch? They are both the same person, from different points in time. Emiya Shirou (the boy) will become Archer (the man).

Browse photography at Denver.Gallery.