Aston said his side, whose only loss came at the hands of Papua New Guinea, had a hard time explaining why they were going home while Samoa would take on Australia for a place in the semi-finals.
"It's disappointing. It's something that probably needs looking at going forward because to win two of three, we probably deserved to go through," Aston said.
"That's how you judge it - go home and tell someone. How do you explain it? That's what we should focus attention on - how do you attract new fans?"
The Irish lost their five-eighth Keyes to a knee injury midway through the first half but did enough to record their second victory of the tournament.
Despite the win, the Irish failed to qualify for the quarter-finals, after finishing second behind PNG in group C.
Keyes suffered a medial ligament strain, prompting a reshuffle with Api Pewhairangi shifted into the halves.
Oliver Roberts, who came on for Keyes, made an immediate impact as he barged over in the 31st minute to make it 12-0.
After Josh Ralph threw a beautiful cut-out pass to set up Ben Morris, Wales suddenly gave themselves a sniff at 22-6 with 20 minutes remaining.
However the Welsh fightback was short-lived as Roberts forced his way over from dummy-half for a soft try in the 68th minute.
The victory was Ireland's biggest in a world cup - surpassing their 36-12 victory over Italy two weeks ago.
