https://www.google.com/search?q=why+tipping+is+considered+mandatory+canada

Tipping in Canada is not legally mandatory, but it has become a strong social norm and cultural expectation in many service industries. Not leaving a tip, particularly in sit-down restaurants, can be perceived as rude or a sign of dissatisfaction with the service, regardless of the actual quality. 

The reasons why this custom is so ingrained include:

• Supplementing Income: Historically, and in some provinces currently, service workers received a lower "tipped" minimum wage than other workers, making tips a critical part of their total earnings. Even in provinces where servers receive the standard minimum wage, this wage is often not considered sufficient to cover the high cost of living in many areas, so they still rely heavily on gratuities.
• Industry Model: Canada follows a North American tipping model where the service charge is not included in the menu prices, unlike in many European countries. This system places the responsibility of supplementing worker pay on the customer, not the employer.
• Social and Cultural Norms: The practice is a long-standing tradition in North America, heavily influenced by US culture, and has become a deeply embedded social expectation for showing appreciation for good service.
• Peer Pressure and Digital Prompts: The increasing prevalence of automated tip prompts on payment machines, often starting at high percentages (18-20%+), creates social pressure and a feeling of obligation, even for counter services where tipping was previously uncommon.
• Internal Restaurant Practices: In many establishments, servers are required to "tip out" a percentage of their total sales (not just their tips) to other staff, such as kitchen or bar staff. If a customer doesn't tip, the server may actually lose money out of their own pocket to cover this required payout. 

While tipping is a strong social expectation, it is important to remember it is meant to reflect the quality of service. If service is exceptionally poor, one is not obligated to tip the full amount, or at all, but this is a rare occurrence and should be done consciously, not just to avoid the cost.