Why is boric acid written as B(OH)3 and not H3BO3?
This is mostly because boric acid is commonly believed to have different acidity mechanism. While common acids generally dissociates

$\ce{HNO3 &lt;=&gt; H+ + NO3-}$

boric acid is commonly believed to associate with water

$\ce{H2O + B(OH)3 &lt;=&gt; H+ + [B(OH)4]-}$

this type of acidity is rather common for metal hydroxides, hence the way of writing.

For that matter, not every hydrogen should be written at the beginning of a formula of an acid, but only actually acidic ones. So, $\ce{H2SO4}$, but $\ce{HPH2O2}$