Fewer people, lower cost are the advantages. Downside is the rain and the heat. But there is not so much of either.
This is day 14 in Thailand. One day had rain most of the day, sometimes heavy. Most of the days had either no rain or it rained late at night. Mostly when it rained the showers were short and intense and gave warning. Sometimes the cloud conditions are a dead giveaway, often one can see squalls to windward that will soon be here and almost always there is a sudden and strong increase in wind about 5-10 minutes before it rains. Do what the locals do. Find a place out of the rain and hang out til it’s over.
The overcast skies makes for lower temperatures. Not down to winter temps but noticeably less than sunny day in the rainy season temps.
Worst thing about the rainy season for me is the lack of bright sunlight. Overcast skies makes for flat photographs during the day and no dramatic lighting near sunrise and set. That’s a fair trade off for 1/3 of the people and half the cost of lodging.