This is why sometimes prayers are not immediately answered by Hashem, as this encourages people to sustain their connection with Him, a connection which would otherwise weaken over time. But for someone who undertakes to continue talking to Hashem even after his wish is granted, there is no reason for the yeshu'ah to be hindered anymore.
The Arvei Nachal writes that this method was adopted by Dovid Hamelech, who implored (תהלים פו ג) חָנֵּנִי ה' כִּי אֵלֶיךָ אֶקְרָא כָּל־הַיּוֹם - Be gracious unto me, Hashem, for unto You do I call all day. The Arvei Nachal elucidates that with this, Dovid expressed his determination to continue calling upon Hashem regardless of the immediate fulfilment of his wishes, thereby enabling his desires to be fulfilled promptly.
(ערבי נחל וארא דרוש א ד"ה יוצא מכלל)