Blinking LEDs are usually reset by the voltage dropping to zero then coming back on. So if one LED, probably the fastest one, blinks first, all the rest in the series string will be reset, then comeback on again when the fastest one comes back on. So you have essentially a single blinking LED and the rest never get to complete the blink cycle. 😱😱
Also, if you connect a blinking LED to a source of fast pulsing DC, like 3 to 5 volts AC through a rectifier, then the blinking LED will look like it’s on steady because it just gets reset 60 times a second.