Regardless of the company's culture, teams should think of their sense of personal integrity and pride in delivery to overcome this ScrumBut practice. The sprint retrospective is a good place for the team to address this.
Remember that the ultimate determination of whether or not failure to meet sprint commitments is acceptable behavior is up to the team. The ScrumMaster can force neither a team nor individuals to adopt a set of values that drive their behaviors. The team must want to make this change on its own. It takes a confident ScrumMaster to hold up a mirror to the team and be willing to ask the questions that will make the team consider its actions and the ramifications. Asking the team, "Is it OK for us to make a promise and then break it?", undoubtedly will make the team feel uncomfortable, but it is a fair question.
The ScrumMaster also may want to make sure that the team is aware of the five values of Scrum: Commitment, Openness, Focus, Respect, and Courage. You can try an exercise with the team using the template "We believe in (value), therefore we will (do something)." Ask the team members to brainstorm on what they believe in and what they plan to do about it. An example outcome from one team might be "We believe in Respect, therefore we will not raise our voices in anger but instead will discuss our differing viewpoints calmly and with open minds." Or, for this particular ScrumBut issue, a team may come up with "We believe in Commitment, therefore we will do whatever it takes to deliver on our promises to the business and to our customers." Using the five Scrum values as a starting point, the ScrumMaster can lead the team in the creation of a set of team working agreements, or value statements, that will drive its behaviors. The team creates these, and the ScrumMaster facilitates the discussion.
Later, if the team reverts to old habits and once again takes a laid-back approach to Commitment, the ScrumMaster can simply ask the team, "Is this in keeping with our working agreement on Commitment?" Part of the ScrumMaster's job is to remind the team of the decisions it made.
Don't accept persistent failures to meet sprint commitments. Question why and how the team came to accept this behavior as normal, and together make a real commitment to change for the better.
For more info on the "ScrumBut" and "We suck less" phenomenon, see Michele's previous article "Little Scrum Pigs and the Big Bad Wolf."