"Rabbi Eliezer then said to them: If the halakha is with me, the walls of the study hall will prove it. The walls of the study hall leaned inward and began to fall. Rabbi Yehoshua scolded the walls and said to them: If Torah scholars are contending with each other in matters of halakha, what is the nature of your involvement in this dispute?.." Bava_Metzia.59b
In the famous argument, R' Yehoshua didn't intervene with the Cherub tree or the stream, however, he scolded the walls. I couldn't find comments on that.
Why did he suddenly care about the walls? Why after the two miracles did he expect the walls to behave differently upon R' Eliezer's request?