Define lucrative, and for whom?
Today, H.R. Harmer Inc. auctioned off part 10 of one man's collection, with total proceeds for this one sale adding up to over 3 million dollars.
The auction house has an 18% commission, meaning that they were paid at least $540,000 for the privilege of selling this collection. Not bad for a day's work.
We don't know what this collector paid for these items, but as noted in another thread, some of these same items sold for more money in the past. This is a hobby, it should not be treated as an investment or you may be disappointed.
That said, there are a lot of hobbyists and part-time dealers having fun and making some income selling stamps and other collectibles on
ebay. It appears to be quite a lucrative business for some of them. The Covid pandemic lockdown seems to have created a burst of activity for the stamp hobby.
From what I understand, the real hay-day and top of the market was the 1980s, when prices across the board were a lot higher than today, not even taking inflation into consideration.
Prior to that, I would say the peak of stamp collecting popularity across the general public was the 1930s when FDR was president and that continued through the 1950s.