font size remains unchanged even though I have used \fontsize{8}{9.6}\selectfont

Question

The font size remains unchanged even though I have used
\fontsize{8}{9.6}\selectfont

MWE:

\begin{frame}
    \begin{align}
    \fontsize{8}{9.6}\selectfont
    \frac{\partial^2 l}{\partial \gamma^2}=&\sum_{i=1}^{n} \delta_{E_i}\bigg[-\frac{e^{\beta_0+\beta_1 x_{i1}}}{\gamma}\bigg(t_i e^{\gamma t_i}\bigg(t_i-\frac{1}{\gamma}\bigg)-\frac{1}{\gamma^2}(1-e^{\gamma t_i})\bigg)
    \nonumber\\
    &+\frac{e^{\beta_0+\beta_1 x_{i1}}}{\gamma^2}\bigg(t_i e^{\gamma t_i}+\frac{1}{\gamma}(1-e^{\gamma t_i})\bigg)\bigg]\nonumber\\
    &+\delta_{R_i}\bigg[-\frac{e^{\beta_0+\beta_1 x_{i1}}}{\gamma}\bigg(t_{Ri} e^{\gamma t_{Ri}}\bigg(t_{Ri}-\frac{1}{\gamma}\bigg)-\frac{1}{\gamma^2}(1-e^{\gamma t_{Ri}})\bigg)
    \nonumber\\
    &+\frac{e^{\beta_0+\beta_1 x_{i1}}}{\gamma^2}\bigg(t_{Ri} e^{\gamma t_{Ri}}+\frac{1}{\gamma}(1-e^{\gamma t_{Ri}})\bigg)\bigg]\nonumber\\
    &+\delta_{I_i}\bigg[-\frac{e^{\beta_0+\beta_1 x_{i1}}}{\gamma}\bigg(t_{Ri}^2e^{\gamma t_{Ri}}-t_{Li}^2e^{\gamma t_{Li}}-\frac{1}{\gamma}(t_{Ri}e^{\gamma t_{Ri}}-\nonumber\\
    &t_{Li}e^{\gamma t_{Li}})-\frac{1}{\gamma^2}(e^{\gamma t_{Ri}}-e^{\gamma t_{Li}})\bigg)+\frac{e^{\beta_0+\beta_1 x_{i1}}}{\gamma^2}\bigg(t_{Ri} e^{\gamma t_{Ri}}-\nonumber\\
    &t_{Li} e^{\gamma t_{Li}}+\frac{1}{\gamma}(e^{\gamma t_{Ri}}-e^{\gamma t_{Li}})\bigg)\bigg]\\
    \nonumber
    \end{align}
\end{frame}