https://duckduckgo.com/?t=ffab&q=soil+ph+availability+chart&iax=images&ia=images
you can find numerous references that show Ca will be fine at 7.6.
soil can buffer and help regulate pH. This is not news, either. The more 'shit' in solution, the tougher it is to move the proverbial needle. i.e. RO will be more susceptible to ph-drift than 300ppm tap water. That does not make tap water better, it just is causality of this relationship.
if there's 10x more things diluted and have the same pH, the large amount of solutes makes it more difficult to shift the pH.
https://pressbooks.online.ucf.edu/chemistryfundamentals/chapter/ph-and-poh/
h30 and oh concentrations are outcomes of acids/bases dissolved in water. they are used to calculate pH. h30 and oh will cancel out and results 2 (molecular ratio) of h2o. this is how acids and bases neutralize each other. After that, the log of what remains after canceling each other out is the pH. or, negative log, whatever the equation says, lol. specifics are not needed here, just the gist.
the point is you can have the same pH with drastically varying amoutns of solutes and if the solute levels are lower, pH drift is easier to occur. it takes less of 'something' to throw it off. products of microbes or things you add with water etc.