Modern smartphones have a lot of constraints to deal with and still meet consumer demand. People want large displays, all day battery life, no slow downs, fast wireless, and the phone needs to fit in a normal pocket. Oh and the phone should be durable against drops and immersion in water.
A large display, fast processor/GPU, and wireless are all battery hungry components. These require a large battery to not only supply enough amperage but have enough capacity to last more than a few minutes. Batteries heat up when charging and when discharging. Things that heat up need to expand. The electronic components also heat up with usage further complicating the thermals. Vents and fans are untenable in something held in one hand or put in a pocket. The total envelope of the phone is constrained by human hands and pockets.
The modern "sealed" smartphone design exists because it satisfies those constraints. Non-removable batteries can have much thinner outer packaging than removable ones. They don't need to resist drops and punctures and still get underwriting certification. Glued components don't tend to wiggle themselves loose after years of thermal exercise. Glue with more seamless casings increase water resistance and overall durability. Glue also allows for smaller contact surfaces than are possible with screws giving more volume to internal components.
A phone that is easy to disassemble will be much less durable than one that's sealed. In the common case where internal access is never required, the durable phone will be superior to the easy to disassemble one. User serviceable batteries need thicker more durable envelopes which means lower power density than fixed batteries.
Most consumers do not want the easily repaired phone. It's going to require a lot of performance and ergonomic trade offs over the sealed flagship phones. Even if people went for repairable phones en masse it's not like they would stay out of landfills.
Even if screws over glue halved the effort to replace a broken screen the component cost wouldn't change. So a repair might be a few tens percent cheaper to perform. Even passing the savings on to a customer, it's still likely someone with a broken screen or whatever phone-ending damage would just buy a new phone.