When 'become' is not becoming

Full-day school becomes an important issue because it concerns a wide range of people, especially parents.

This is the influence of Bahasa Indonesia. In English 'become' is always used to describe a change, rather than a constant:

People become sleepy when they drink a lot of beer.
Most knives become dull after a while and need to be sharpened.
When there's a problem, Clark Kent becomes Superman.

In each of these three cases, a change is implied:

..from alert to sleepy
..from sharp to dull
..from newspaper journalist to superhero

These are all familiar, recurring situations, and so we use present simple tense to describe them.

If we say "Full-day school becomes an important issue," a change is indeed implied (from non full-day school to full-day school), but since this is a unique, rather than a recurring situation, then we need a time frame.

If the change happened in the past, but we're not sure exactly when, then we use present perfect tense:

Full-day school has become an important issue.

If the change is happening right now - continuously - then we can use present continuous tense:

Full-day school is becoming an important issue.

However, if we are analysing a situation that is true now, constant and without change, as though we are looking at it under a microscope, then we use present simple tense:

Full-day school is an important issue.