Sometimes I think maybe they are scared by the hustle and bustle here.

If you are out and about, you canwill only see the streets all packed with people, which makes me feel a bit suffocated.

you could include "all" and it would be just fine. I just wouldn't put it there. It sounds redundant.

I do thinkget they have reasons to not to show up in the city centrer (american eng.)!

However, if you live in a supeburb, you still have got a chance to see them.

grammatically, this is not correct... but It sounds 100% natural. You could also say: you've still got a chance to see them.

I once saw one.saw one once. (american eng.)

AIt was a tiny green dot was flying briskly, i. It seemed it was dancing with the leaves straggling all over the place, rustling in the breeze.

Fireflyies

Fireflies are pretty uncommon in my city.

Sometimes I think maybe they are scared by the hustle and the bustle here.

If you are out and about, you can only see the streets all packed with people, which makes me feel a bit suffocated.

I do think they have fireflies have their reasons for not to showing up in the city centre!.

Do not use "they", as "they" may still be referring to the streets, not the fireflies. Use "they" only if it is describing the last thing you wrote.

However, if you live in athe supeburb, you may still have gota chance to see them.

I once saw one once.

AIt was a tiny green dot was flying briskly,. it seemed like it was dancing with the leaves, straggling all over the place, and rustling in the breeze.

Fireflyies

Sometimes I think that maybe they are scared by the hustle and bustle here.

If you are out and about, you can only see the streets all packed with people, which makes me feel a bit suffocated.

I do think theyfireflies have reasons not to show up in the city centre!

However, if you live in a supeburb, you still have gotget the chance to see them.

A tiny green dot was flying briskly, it seemed it was dancing with the leaves stragglfluttering all over the place, rustling in the breeze.

Sometimes I think that maybe they are scared by the hustle and bustle here.

If you are out and about, you can only see the streets all packed with people, which makes me feel a bit suffocated.

You're is commonly used instead of you are.

I do think they have reasons to not to show up in the city centre!

However, if you live in a supeburb, you still have gota chance to see them.

A tiny green dot was flying briskly, i. It seemed like it was dancing with the leaves straggl, flying all over the place, rustling in the breeze.

I changed "straggling" because straggling is when someone is falling behind a group.

Fireflyies

Sometimes, I think maybe they arthey may be scared by the hustle and bustle here.

https://www.grammar.com/maybe_vs._may_be#:~:text=Maybe%20or%20may%20be%3A,be%20is%20a%20verb%20phrase.&text=Remember%20the%20spaced%20word%20are,a%20verb%20in%20a%20sentence.

The ubiquitous high-rise buildings block out the sun.

I know what you mean here, but this isn't quite the right usage of the word "ubiquitous."

If you are out and about, you can only see the streets all packed with people, which makes mecan feel a bit suffocateding.

The first part of the sentence is "you," so it doesn't make sense to switch to the first person (makes me feel) at the end. You could also write:

"If you are out and about, you can only see the streets all packed with people, which might make you feel a bit suffocated."

I do think they fireflies have reasons not to show up in the city centre!

However, if you live in a supeburb, you may still have gotthe chance to see them.

You can say "have the chance" or "get the chance."
Suburb = residential area outside the city.
Superb = extremely good :)

A tiny green dot was flying briskly, i. It seemed it wasto be dancing with the leaves straggling all over the place, rustling in the breeze.

Again, the word "briskly" isn't quite right for this context. I don't think I've ever heard "straggle" used as a verb.