Masonry products and materials are by far the most durable construction materials available, especially when installed by quality contractors who employ trained, skilled craftworkers.
Mortar joints are serviceable for 35 years or more when properly installed.
Masonry units themselves (typically brick or concrete block) may have a serviceable life of 100 years or more.
Masonry is subject to weathering like any other building product continuously exposed to the elements. Acids in the rain, seismic movement, building settlement and freezing and thawing cycles impact damage and dirt … All of these conditions take their toll.
When visual inspection reveals that the mortar joints are cracking or have otherwise deteriorated, restoration is necessary to help maintain the integrity of wall systems and products. Tuckpointing is an effective way of decreasing water entry into masonry.
Your local historic and/or preservation society is a good resource for free advice before you begin talking with contractors about a masonry project.