problem with tenses

hello Teachers,

I have a problem with what tesnses I should use while describing a picture.
I've been tought that I should use present tenses, especielly present continuous.
ex.
He is sweeping the street etc.

Why the sentence below is correct? (The sentence describes what is in the picture).
The bus has tilted to one side because of the fact that there were too many people on it and they were distributed unevenly.

Why do we have to use in the above past tense , I mean ' there were too many people' and 'they were distributed ' , why can we not use 'are' instead of 'were'.

Does the sentece mean that the bus is already empty? and if so, should we use present tense ( with 'are') if the bus is still full with people?

thank you

[Tdol]

The bus still has the people, but the important event, what made the bus lean to one side occurred before the picture 'was taken'.