How do surface mount components withstand heat of reflow while through hole components can not?

One of the key points to answer your question is thermal stress. When you apply heat to one pin of a device, there is a suden and huge temperature difference between that point and the rest of the device. That difference is stress, and the result can be a material breakout.

On an oven, on the other hand, all the board is put under a controlled, gradual thermal rise. ALL the points of the device are at almost the same temperature, so there are no thermal stresses (or they are much smaller than) they were when you applied the soldering tool to ONE pin and the rest of the device is at room temperature.

TO-92 and similar types of through-hole transistor packages are not that temperature sensitive. They're soldered by running the bottom of the PCB over a fast-flowing river of molten solder which transfers heat rather quickly. The boards are typically preheated a bit, but only to about 100°C.

Here is a video of wave soldering. The vapor you see coming off the board is mostly from the flux.

Some parts are just unsuitable for reflow soldering because of the type of plastics used, or other material concerns. In some cases they have been adapted by using more expensive plastics, in other cases there is no solution because the plastic is part of the component- for example there are no SMT polystyrene capacitors because of the low melting point of PS. There are SMT film caps using dielectrics such as PPS (Polyphenylene Sulfide) but they're not necessarily as good performing (especially with regard to dielectric absorption).