Which exchange?

Stellar has  lot it seems of arbitrage bots wtching for chances to use Lumens to buy something with which to buy something else with which to buy something else to then sell for more Lumens than they started with, so if you are talking about Stellar that could be what you are seeing, also on Stellar we have "Kelp" free open source bot that they provide doing market-making on all the Galactic Milieu currencies on Stellar.

If on FreiExchange though I don't think there are any bots there.

It can be hard to buy simply because price is so insnely low right now, especially compared to calculated value based on treasuries; the only reason any at all are anywhere close to such low prices is market-makers getting them even cheaper when folks "dump" onto their buy offers.

Some of the market-makers offer the cheap coins they get that way back on sale with an ascending column of sell offers starting not too horribly far above the highest buy offer to lure people upward, since they make a profit anyway some prefer not to make buyers go all the way up in one bite to the actual calculated value.


-MarkM-