Why most IC are active low?

Answer 1

Most control signals in electronics are active-low signals (usually reset lines, chip select lines and so on). This stems from the fact that most logic families can sink more current than they can source, so fanout and noise immunity increase. (The reason for this is ultimately related to the fact that electrons are negatively charged.) It also allows for wired-OR logic if the logic gates are open-collector/open-drain with a pull-up resistor. Examples of this are the I²C bus and Controller Area Network (CAN).

Answer 2

in case of TTL compatibility gates there can be three inputs one is HIGH input,LOW input and the input may be OPEN( i.e.neither Low nor high). In such case High and open inputs gives out the same output. such as if we have NOT gate of TTL family if the input is HIGH or OPEN the output will be LOW. so if there will be an active high Read signal to a microprocessor if the read wire is coincidentally broken it will be taken as OPEN input or HIGH input (as both are the same) so we are not actually sending the read signal but the microprocessor is getting the Read signal which is not desirable.So we made the Read signal to be active low so that it will be activated only if it will be low, neither during it is high, nor when it is open.