Obesity tends to involve large amounts of processed foods in the diet: not only full of excessive [and bad kinds of] fats, salt, and sugars, but also artificial sweeteners, colors, preservatives, and other additives. These are thus full of chemicals, just plain don't break down right, and contribute to non-alcoholic fatty liver disease (NAFLD) - the liver overwhelms and collects fat in its cells it fails to break down. Conversely, fruits and veggies replaced by junky foods are full of various vitamins and minerals that would support liver function - if only consumed(1). On a further food note, trickles of commonly-present genetically-modified (GMO) corn and soy will cause cleansing organs like the kidney and liver to fail(2).
Sleep deprivation cuts the efficiency of the liver to process fats, thus causes fats to accumulate there, and prevents the vital self-repair mode of the body.
Smoking means horrid chemicals worm their way into the liver and cause oxidative stress - so much so that the liver produces scar tissue fighting the free radicals.
Why is alcohol the top liver damage agent? The liver ends up spending a whole bunch of its energies breaking it down and converting it into something else, gets drawn away from dealing with other toxins, and develops cancer in the process. Some damage may end up permanent.
Tylenol (acetaminophen) is a well-known liver-taxing medicine - in particular, several days of heavy use can be all it takes to wreak liver havoc. Various other medications also induce liver issues. Way too much of certain nutrients tends to be why certain herbs and supplements may tax the liver. This is one extra reason to check labels on both meds and supplements: for warnings of liver failure, etc.(1)
Sources:
1. Hills, Jenny. "5 Things You’re Doing that are Killing Your Liver (MANY People DO Them)." Healthy and Natural World. Web. 6/17/19, https://www.healthyandnaturalworld.com/common-habits-that-damage-your-liver/.
2. "Gilles-Eric Séralini." TruthWiki: Get the Real Story, TruthWiki, approximately 4 years ago. Web. 6/17/19, http://www.truthwiki.org/gilles-eric-seralini/.