Because it makes initial connection much slower. Dumb switch - you insert a cable and it works. STP-enabled switch: you insert a cable and it takes a while until the port is enabled (unless you do extra configuration, appropriate for your network topology). This is annoying and for inexperienced users it could seem like the switch ‘does not work’. It is easier to sell a switch without such a feature enabled by default.
Because it makes initial connection much slower. Dumb switch - you insert a cable and it works. STP-enabled switch: you insert a cable and it takes a while until the port is enabled (unless you do extra configuration, appropriate for your network topology). This is annoying and for inexperienced users it could seem like the switch ‘does not work’. It is easier to sell a switch without such a feature enabled by default.