ANSWER:

Because this intention was to make the reward for the parents. If his intention is to share it with them, this would be like building half a masjid for him and the other half is for them. 

Sheikh on your twitter someone asked who will get the reward of building a mosque when someone builds the mosque with the intention that the deceased parents get the reward and he names the mosque after them and you said only the parents get the reward. Why? Why doesnt the one who builds it also get a reward?