Why the magnitudes values in magnitude spectrum are different even though the amplitudes of the signals are same

Here I have a combined sinusoid(y). It's a combination of two sinusoids one with 7Hz(x1) and one with 40Hz(X2), Amplitudes of both signals are same.

But combined sinusoid's magnitudes values in magnitude spectrum is different.

Why is that?

%code begins

close all;

clear all;

fs = 250;%sampling frequency

N = 1000;%number of data points

W = 2*pi/N;%frequency in rad/s

t = 0:1/250:4;% ;%time index

x1 = sin(2*pi*7*t);%7 hz sinusoid

x2 = sin(2*pi*40*t);%40 hz sinusoid

y = x1+x2;%adding two sinusoids

l = fft(y);

%plotting

figure,plot(abs(l)) ,title('Magnitude Spectrum');

xlabel('Frequency Number'),ylabel('Power');

%code ends