Why \underbrace and \overbrace create brackets with gaps?

Question

I noticed that when we use \underbrace and \overbrace, it creates a bracket that is assembled by several parts, please see the picture below demonstrating what I mean:

If we zoom in, we can see:

And

Which causes a small inconsistency, and I am puzzled because this is not a glitch, it's how the package made it to be, I just wonder if there's any reason why they make it this way?

Here is a minimal working example:

\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
$\underbrace{\left(A_{N} \cdot \int_{\left(m_{-i}, v\right)} \frac{v}
{\operatorname{rank}\left(m_{i} ; m\right)} \rho\left(d m_{-i}, d v | 
m_{i}\right)-X_{N}, t_{i}(1)\right)}_{ \leq A_{N} \cdot 
t_{i}^{\prime}\left(m_{i}\right)-X_{N}=t_{i}\left(m_{i}\right) \text { if } m_{i}<1}$
\end{document}

Answer 1

My proposal is only an aesthetic alternative using, for example, \undercbrace from lite mtpro2 package. I have reconsidered some changes of your original code.

\documentclass[12pt]{article}
\usepackage{newtxtext,mathtools}
\usepackage[lite]{mtpro2}
\begin{document}
\[t_i(m_i)\geq \min\undercbrace{\left(A_N\cdot \int_{m_{-i},v} \frac{v}{\operatorname{rank}(m_{-i};m)}\rho(dm_{-i},dv\mid m_i)-X_Nm t_{i}(1)\right) }_{\leq A_{N} \cdot t'_{i}(m_{i})-X_{N}=t_{i}(m_{i}) \text { if } m_{i}<1}\]

\end{document}