So let me whine for a bit about LaTeX. LaTeX is document-preparation software used a lot in the sciences - in the mathier sciences particularly. The basic idea is that you have a source file, you feed it into the LaTeX processor, and it spits up a PDF. The reason you'd do this is because LaTeX is really good at type-setting math - way better than any other software I know of, anyway.
Essentially, it turns a source file that looks something like this:
\documentclass[11pt]{article}
\begin{document}
Do you seek knowledge of squid giant axons?
\[ C_m \frac{dV \left ( t \right )}{dt} = \sum_i I_i \left ( t, V \right ) \]
\end{document}
into this:
.
LaTeX is also the math-language for wikipedia, which some of you have probably guessed (or a sub-set of it is, I'm not sure).
If you have a lot of math to lay out, LaTeX is your baby. The problem is that there's more to modern documents than laying out equations nicely. You see, LaTeX is old: the current major version of LaTeX is LaTeX 2e, which had its first release in 1994 and its last release in 2011. There are a lot of things that modern users expect to be able to do easily when making a document that LaTeX doesn't nicely support - like embedding images, having colored text, setting your page margins or including source-code listings.
One or two people reading this post just yelled "Hey, wait a minute! LaTeX can do all of those things!" Sort of; straight-up LaTeX can't, but there are
packages that add all of those features. Sometimes, in fact, more than one package; consider the
wikibooks section on including source-code listings, or the
wikibook chapter on embedding graphics, or the
wikibooks section on typesetting algorithms. (Would you call that
simple?) Notice that in the case of both graphics and algorithms, there are
multiple packages that do
the same job in different ways - and sometimes there are even packages that extend other packages!
The problem, essentially, is that the needs of LaTeX users have changed, but the core system has not evolved at all; it's still more-or-less the same LaTeX 2e we've had since 1994. To fix this, people have been releasing more and more packages to shore up the capabilities of the basic system; however, even these packages have aged out usefulness, and other packages have sprung up to add in
even more features that the previous crop of packages didn't include.
In an ideal world, what it would be nice to do is throw out the mess that is LaTeX 2e and rebuild it for the current, completely different environment; sadly, that's impractical for a number of reasons. Among them are all those goddamned packages; people are actually using those things right now in their documents. If the LaTeX authors started over, they'd either have to either maintain compatibility with all those packages (which'd be a nightmare) or provide as much of the functionality of those packages in their new system (which'd be a herculean engineering challenge). There is in fact a project to build a new version of LaTeX,
LaTeX 3; that's going nowhere, I suspect largely for the reason that they can't possibly satisfy all the needs that the old, decrepid LaTeX 2e plus its 80 bajillion mutually incompatible packages is currently handling (however poorly it's handling them).
So we're stuck with the same old typesetting system, which makes it easy to typeset equations in exchange for making it hard to do God-damned near anything else.
Edit: None of this even touches the less-than-intuitive and inconsistent syntax, or the sometimes-crazy layout rules (like the ones governing figure placement), or that its default behaviors and settings can be insanely hard to change without using packages, or the way it can shit the bath if a figure or table is wider or higher than a page.