I believe that that graph is adjusted for Urban CPI so so increased costs would be taken into account. It's also a bit difficult to see the change in median household income due to the scale so here's the federal reserve's version where it is easier to see[1]. The increase in real median household income has been significant since the mid 80s. There are plenty of factors in play but I don't really think stagnant wages relative to other countries are to blame for fewer American tourists. Honestly, I just don't know many people in the U.S. who would think to vacation to Malaysia. The Caribbean is a lot closer and less expensive to travel to.
[1]https://fred.stlouisfed.org/series/MEHOINUSA672N