Why are the letters in print like ‘a’,’g’ etc. different from the way we write?

Because when we write, we use either flowing cursive or hand printing that is intended to be easy to write, while print letters are harder to make, but have been worked out for centuries (typography) as being easier to read accurately. A kind of writing called calligraphy, which takes 2-3 times as long to write is done like type faces and was used for writing manuscripts (manu=hand) before loose type printing was invented.

I write my a’s like that

it’s just the font

there are also fonts that look like the way we write it as.