It is under the circumstances. Wallace was a regional candidate, basically confined to the south. Wallace won five states, Louisiana, Arkansas, Mississippi, Georgia and Alabama. He also raised a lot of money, most of it spent in the south. Wallace had name recognition, media coverage, lots of media coverage, was well known. Anderson, didn't have that much money. But his being in a debate with Reagan gave him name recognition nationwide, he also had media coverage. Like Wallace people know who he was and what he stood for.
Perot, he had money. He spent 300 million of his own money back in 1992. He appeared in all three of the presidential debates, his message about the national debt was well publicized in the media. As was him. People know who they were voting for when they pulled the lever for him. In 1996, Perot wasn't allowed in the debate, hence his stature and vote getting ability dropped from 19% to 8%. He didn't get much media coverage in 96, the media focused on Clinton and Dole.
In 2016, unlike Wallace, Anderson and Perot, Johnson, Stein, Castle, other third party candidates had no name recognition, no media coverage, participated in no debates, no one knew who they were. They were totally ignored by the media, no political advertisement, no nothing. The only reason one would vote for a third party candidate one didn't know, had no idea what they stood for, was their last name wasn't Trump or Clinton. Six percent is nothing. Give that six percent to Clinton and she would have had 54% instead of 48% of the total vote. 6% for no nothings in 2016 is very significant. 1.5% for no nothings in 2012, 1.4% for no nothings in 2008, 1.0% for no nothings in 2004. See a pattern here.
To make matter worst, money if you will, Clinton spent 1.4 billion dollars, Trump 957.6 million, the most any third party candidate spent was Gary Johnson who spent 3 million. That makes Johnson and the others no nothings. No way to get their message out.
https://www.washingtonpost.com/graphics/politics/2016-election/campaign-finance/