Factors that weaken the competitive pressures created by rivalry among competing sellers include

There are several factors such as high consumer demand. If there is a lot of demand, rival firms will still have plenty of sales on their own. If there are high costs of switching brands, consumers will stick with what they have rather than going to a rival (gym memberships have sign up fees, monthly costs and contracts so it costs a lot to switch. Even though there are many competing gyms, people will generally stick to the one they have).

Having a higher number of rivals also increases the odds that one rivals actions will have a major impact. If there are 2 places selling ice cream and one has a sale, the other will lose business. If there are 200 ice cream shops and one has a sale, people will likely not even notice because there are so many other places they can try.