Bell has yet to sign his $12.12 million franchise tender and, as a result, is not subject to fines for his no-show.
The two sides couldn't reach a long-term agreement before the July 17 deadline, which Bell told ESPN was "a little frustrating, but it's a business."
Steelers receiver Antonio Brown reiterated to reporters what he said on social media in a direct message to Bell: The first part of getting better is showing up.
"When trying to do something special, we would like all our guys here," Brown said Thursday.
Other players took a softer approach, acknowledging they would like Bell in camp but understand the business side.
"The biggest thing with football, no matter who you are, this thing moves on without you," guard David DeCastro said. "It's kind of an unfortunate truth, but it is the way it is. If he's not here, we've got to go."
Addressing the media after the Steelers' conditioning test Thursday, coach Mike Tomlin said he has had "good, clean communication" with Bell recently but wouldn't divulge the nature of the conversations.
"Obviously we'd like him to be here," Tomlin said. "I'm going to focus my energies on the guys that are [here]. ... It's an unfortunate circumstance." Bell stays in good football shape throughout the calendar year but rust could be an issue and "there's no question" the Steelers value the team-building that Bell will miss, Tomlin said. When asked about the consequences of Bell's missed time, Tomlin said they are "untold as we sit here."
Left tackle Alejandro Villanueva, who was also without a contract, reported to camp after the Steelers signed him to a four-year deal Thursday afternoon.
Bell has a precedent to follow: Chiefs safety Eric Berry reported later in August to sign his tender last summer, then had a big year and signed a six-year, $78 million extension this offseason.
Bell, 25, was a second-round pick in 2013. He has been elected to two Pro Bowls and has rushed for 4,045 yards despite missing 17 regular-season games over the course of four seasons.
Center Maurkice Pouncey says Bell is a unique talent who doesn't need practice every day, but the benefit of reporting is "just to be around the team, so you guys don't have to ask the same questions every day. He could sit on the sidelines and answer those questions."
In other Steelers news, wide receiver Martavis Bryant is not eligible to practice because he's still under conditional reinstatement with the NFL over substance abuse violations.
Bryant has missed 20 games over the past two seasons for drug offenses. In late April, the league made clear he could be with the team on a conditional basis and had hurdles to clear.
A source says Bryant is with the team right now and is working to finalize his reinstatement in the coming days or weeks.
"Upon his conditional reinstatement in April, Martavis Bryant was made aware it was only the beginning of a process toward a return to being a full contributing member of the Pittsburgh Steelers," general manager Kevin Colbert said in a statement.
"We have been informed by the NFL that Martavis is still in the process of being fully reinstated. Until that time, Martavis will be permitted to take part in off-the-field team activities at training camp, but he will not be permitted to practice or play in any games."
Tomlin said he knew it was possible for Bryant to miss time and the circumstance is more procedural than the player having suffered a setback. Bryant was eligible for offseason workouts but training camp was a different matter.
"What we will continue to do is cooperate [with the league] fully," Tomlin said.