Chelsea, who beat Manchester United 4-3 at home on Thursday, opened the scoring at Bramall Lane through Thiago Silva but were pegged back when Jayden Bogle netted before half-time.
Noni Madueke restored Chelsea's lead in the 66th minute before Blades' striker Ollie McBurnie snatched an equaliser in stoppage time.
Chelsea also dropped points in a 2-2 draw with relegation-threatened Burnley at the end of last month and Pochettino said the packed schedule was taking its toll.
"Of course, they were tired but that is not an excuse today not to win the game at the end," he told reporters after the match.
"Watching football, as a 52‑year‑old, you identify very quickly when a team is ready to compete or not.
"Maybe because this group is still not mature enough to compete every single game, every three days ... because like you say Sheffield is in the relegation zone.
"I'm not saying we're not being respectful, but we need to think a little bit more."
Pochettino also said he took top scorer Cole Palmer off in the 74th minute as a precaution.
"We need to protect him," he added.
"We wanted to give him some rest and try to avoid some problems in the future."
Chelsea, who are ninth, next host Everton in the league before playing Manchester City in the FA Cup semi-finals on April 20th.
