You know, stock is a very misunderstood medium. There is/used to be this idea that you simply sent off your old pics and that was that - the cheques would just roll in. Well, I never did discover that scenario in real life.
I spent many years with the Tony Stone Associates library (later became Getty), probably the best in the business at the time, with Image Bank keeping very close company as did FPG International. I used 35mm Kodachrome, mostly, and did have some success. However, there was always the sense that I should upgrade to 6x6 or 6x7 and the consequential problems associated with increased costs, lack of mobility etc. etc. I had a flirtation with Pictor for a short while and they were adamant that 6x6 should be used, and that 6x7 was even better. By the time I realised that Papa Alberto did know best, invested in a Pentax 67, the game had already moved on past me and digital and the internet were taking their toll of the old practices.
But the point I´m trying to make is this: never assume that stock is an anything goes medium. The requirements were high thirty years ago and they are as high today. Though thousands - no, possibly millions of people now swamp the industry, I would wager that it is still a relatively small number of photographers that makes the necessary investments in time, effort, money and skills that has all the luck. Luck, as in the more seriously that group takes the business, the harder it works, the luckier it gets!
I have no knowledge of Alamy but imagine that they face the same realities as do the top stock people too. With falling prices across the board, why would clients still need to hunt bargain basement?