Espressif's ESP32 line uses an MCU IC, either sold by itself (https://www.espressif.com/sites/default/files/documentation/...) or with flash memory and RAM ICs, all packaged together in a system-in-package footprint. (e.g. https://www.espressif.com/sites/default/files/documentation/...) There are various options for which flash and RAM ICs are packaged together, but the ESP32 die itself is very much an MCU and has only has 520 KB of SRAM.

A managed switch is very computy heavy, and does usually run a microprocessor with a full RTOS, if not Linux itself, which probably costs in the mult-dollar range. It's also not something most people have at home, outside of the switch built into their router. Everything elese you mentioned usually runs on microcontrollers with under 1 MiB of RAM. For example, Infineon's CYUSB306X series ASICs for webcams come in two RAM sizes: 256 KiB or 512 KiB, despite handling gigabits per second of data, and having an MCU at all isn't even necessary. (https://www.latticesemi.com/usb3#_CDED461DE15245C78A2973D4A4...) The Pinecil's Bouffalo BL706 MCU has 123 KiB of RAM, despite being a low-volume product where design time matters more than component cost. (https://wiki.pine64.org/wiki/Pinecil, https://en.bouffalolab.com/product/?type=detail&id=8) Microwave ovens are so high volume that they often don't even use packaged microcontrollers, mounting the die directly on the PCB, with an epoxy blob protecting it, and there's no way any would splurge on megabytes of SRAM. The most advanced microwave oven I've seen was from the 90's and definitely didn't splurge on an microprocessor. (https://www.youtube.com/watch?v=UiS27feX8o0)

A slow MCU with external memory could run anything, like booting into linux on an AVR (https://www.avrfreaks.net/s/topic/a5C3l000000BrFREA0/t392375) but it's going to be extremely slow and not practical for any commercial product, which if produced in any volume will have as little RAM as possible.