This is an interesting development so let me take a stab at it.

It looks like there is a premium on older versions of shock lands, and Temple Garden and Overgrown Tomb are present in some of the more popular strategies in Standard at the moment. The premium is currently around 3 3tix on those cards. Looking at Blood Crypt and Hallowed Fountain, the premium on those cards from Dissension is 7 to 8 tix.

On the other hand, there is Steam Vents from Guildpact. This card has been priced in the 10 to 20 tix range in the last year, but has fallen to 5.44 tix with the RtR version at 4 tix. I’d guess Steam Vents is the least used of all the RtR shocks in Standard at the moment.

I think most of this is explained by how Standard has unfolded. Thus, it’s all a coincidence. If Watery Grave and Sacred Foundry are not used that much (, ie they turn out to be more like Steam Vents), then waiting too long to sell could easily turn a profitable position into a losing one.

Thanks for the question!

One must suppose that after the window you talked about the cards should drop again, but right know the ravnica version of Temple Garden and Overgrown Tomb are still up. For example Overgrown Tomb in supernova is at 8.45, not far from your average of 8.75.

Any idea of why?

Also this could mean that this strategy have even less risk, or at last that’s what it looks like.