... especially on weekends when it is [the] busiest.

[atabitaraf]

"Many shoppers throw food and snack casings onto the sidewalks, and shop owners themselves tend to keep their garbage bags there, as well. Not only is this very unhealthy, but also creates a very unpleasant scene, especially on weekends when it is busiest." (reference: Ebrahim Tahasoni's model letter in his pamphlet for IELTS)

My question is: Why did he write the superlative adjective 'busiest' without the definite article 'the'?

 

[emsr2d2]

"Many shoppers throw food and snack casings onto the sidewalks, and shop owners themselves tend to keep their garbage bags there, as well. Not only is this very unhealthy, but also creates a very unpleasant scene, especially on weekends when it is busiest."

(reference: Ebrahim Tahasoni's model letter in his pamphlet for IELTS)

My question is: Why did he write the superlative adjective 'busiest' without the definite article 'the'?

The article is optional in that sentence.

Note that there is no reason to say "My question is:". Just ask the question!
What exactly do you mean by "pamphlet for IELTS"? A pamphlet is usually a small booklet containing just a few pages. Has this Ebrahim Tahasoni really tried to cram all their advice for the IELTS exam into just a few pages?

 

[atabitaraf]

The article is optional in that sentence.

Note that there is no reason to say "My question is:". Just ask the question!
What exactly do you mean by "pamphlet for IELTS"? A pamphlet is usually a small booklet containing just a few pages. Has this Ebrahim Tahasoni really tried to cram all their advice for the IELTS exam into just a few pages?

1. Yes, removing 'the' seems natural to me too, but why? Is there any grammatical point here?
2. It was from a few pages he put on his website. He did not try to cram all his points in it though. I believe it was a kind of sample answer for advertising his courses.

 

[emsr2d2]

2. It was from a few pages he put on his website. He did not try to cram all his points in it though.

In that case, the source is the website, to which you should have provided a link.

 

[jutfrank]

Here's where I think is a good place to begin to answer your question about whether or not to use 'the' before superlatives.

When the adjective is predicative (when there's no following noun), you can leave the article out:

The town centre is busiest in the morning.
Which of you is hungriest?
Eating it cold is best.

When the adjective is immediately followed by the noun it modifies, you can't omit the article:

The busiest time of day in the town centre is morning.
I'm the hungriest one here.
Eating it cold is the best way.